Droplet operations platform

ABSTRACT

The invention relates to a droplet actuator device and methods for integrated sample preparation and analysis of a biological sample. A droplet actuator device is provided for conducting droplet operations. The droplet actuator device may include a bottom substrate and a top substrate separated from each other to form a gap therebetween; an arrangement of droplet operations electrodes arranged on one or both of the bottom and/or top substrates for conducting droplet operations thereon; a reagent storage layer comprising one or more compartments bound to the top substrate; and one or more openings arranged to provide a fluidic path from the one or more compartments into the gap, upon breach of a breachable seal separating the one or more compartments and openings.

1 RELATED APPLICATIONS

This patent application is related to and claims priority to U.S.Provisional Patent Application No. 61/318,851, filed on Mar. 30, 2010,entitled “Sample-to-Result Molecular Diagnostic Platform,” and61/361,576, filed on Jul. 6, 2010, entitled “Sample-to-Result MolecularDiagnostic Platform,” the entire disclosures of which are incorporatedherein by reference.

2 FIELD OF THE INVENTION

The invention generally relates to a droplet actuator device and methodsfor integrated sample preparation and analysis of a sample, such as abiological sample, for the presence and/or quantity of an analyte.

3 BACKGROUND OF THE INVENTION

A droplet actuator typically includes one or more substrates configuredto form a surface or gap for conducting droplet operations. The one ormore substrates establish the droplet operations surface or gap and mayalso include electrodes arrange to conduct the droplet operations. Thedroplet operations substrate or the gap between the substrates istypically coated or filled with a filler fluid that is immiscible withthe liquid that forms the droplets.

Droplet actuators are used in a variety of applications, includingmolecular diagnostic assays, such as quantitative polymerase chainreaction (qPCR) and immunoassays. Molecular diagnostic assays are usedin a wide variety of settings, such as infectious pathogen detection andpoint-of-care diagnosis. Current microfluidic protocols for samplepreparation typically begin with analyte capture beads suspended in asmall volume (e.g., 250 microliters (μL)) of lysed sample. Individualdroplets are then dispensed and the capture beads are concentrated in asingle droplet over a permanent magnet. However, bead dispensing,concentrating, and washing are time-consuming steps and significantlyincrease the time-to-result of a diagnostic assay. Consequently, newapproaches are needed to achieve rapid “sample-to-result” moleculardiagnostics for point-of-care use.

4 BRIEF DESCRIPTION OF THE INVENTION

The invention relates to a droplet actuator device and methods forintegrated sample preparation and analysis of a biological sample. Usingdigital microfluidics technology, the droplet actuator device andmethods of the invention provide the ability to perform samplepreparation and analysis from a single biological sample on the samedroplet actuator. The droplet actuator device uses a large input samplevolume (e.g., about 1 milliliter (mL)) and provides for rapid captureand concentration of target analytes for subsequent molecular diagnosticassays (e.g., qPCR, immunoassay).

In one embodiment the invention provides droplet actuator device forconducting droplet operations. The droplet actuator device may include abottom substrate and a top substrate separated from each other to form agap therebetween; an arrangement of droplet operations electrodesarranged on one or both of the bottom and/or top substrates forconducting droplet operations thereon; a reagent storage layercomprising one or more compartments bound to the top substrate; and oneor more openings arranged to provide a fluidic path from the one or morecompartments into the gap, upon breach of a breachable seal separatingthe one or more compartments and openings.

In another embodiment, the droplet actuator device and methods of theinvention provide for increased droplet throughput for rapid samplepreparation and analysis. In one example, increased droplet throughputis provided by manipulation of larger sized droplets.

In another embodiment, the droplet actuator device and methods of theinvention provide for efficient and controllable loading (e.g., reliableloading) of a large sample volume (e.g., about 1 mL) into a dropletactuator. In one example, reliable loading is provided by storage of asample in an on-actuator reservoir in an energetically favorable state.

In another embodiment, the droplet actuator device and methods of theinvention provide for effective mixing of analyte capture beads within asample volume of about 1 mL. In one example, electrowetting may be usedto mix a sample stored in an on-actuator reservoir.

In another embodiment, the droplet actuator device and methods of theinvention provide for rapid and efficient concentration and collectionof analyte capture beads, e.g., magnetically responsive capture beads.In one example, one or more stationary magnets may be arranged inproximity of a sample stored in an on-actuator reservoir. In anotherexample, a movable magnet may be used for concentration and collectionof analyte capture beads.

In yet another embodiment, the invention provides a detection systemthat uses a single excitation beam and a single detection beam tocollect multiple (e.g., four) different fluorescent signals at a singledetection spot on a droplet actuator.

In yet another embodiment, the invention provides methods forcontrolling heat flow and minimizing thermal losses in one or moretemperature control zones on a droplet actuator.

In yet another embodiment, the invention provides devices and methodsfor generating heat off-actuator and transferring the heat to designatedtemperature control zones on a droplet actuator.

In yet another embodiment, the invention provides methods forcontrolling the temperature of a droplet by transporting the dropletfrom one temperature region to another temperature region (positiondithering) on a droplet actuator.

Further features and other aspects of the invention are more clearlyevident from the following detailed discussion and from the appendedclaims.

5 DEFINITIONS

As used herein, the following terms have the meanings indicated.

“Activate,” with reference to one or more electrodes, means effecting achange in the electrical state of the one or more electrodes which, inthe presence of a droplet, results in a droplet operation.

“Bead,” with respect to beads on a droplet actuator, means any bead orparticle that is capable of interacting with a droplet on or inproximity with a droplet actuator. Beads may be any of a wide variety ofshapes, such as spherical, generally spherical, egg shaped, disc shaped,cubical and other three dimensional shapes. The bead may, for example,be capable of being transported in a droplet on a droplet actuator orotherwise configured with respect to a droplet actuator in a mannerwhich permits a droplet on the droplet actuator to be brought intocontact with the bead, on the droplet actuator and/or off the dropletactuator. Beads may be manufactured using a wide variety of materials,including for example, resins, and polymers. The beads may be anysuitable size, including for example, microbeads, microparticles,nanobeads and nanoparticles. In some cases, beads are magneticallyresponsive; in other cases beads are not significantly magneticallyresponsive. For magnetically responsive beads, the magneticallyresponsive material may constitute substantially all of a bead or onecomponent only of a bead. The remainder of the bead may include, amongother things, polymeric material, coatings, and moieties which permitattachment of an assay reagent. Examples of suitable magneticallyresponsive beads include flow cytometry microbeads, polystyrenemicroparticles and nanoparticles, functionalized polystyrenemicroparticles and nanoparticles, coated polystyrene microparticles andnanoparticles, silica microbeads, fluorescent microspheres andnanospheres, functionalized fluorescent microspheres and nanospheres,coated fluorescent microspheres and nanospheres, color dyedmicroparticles and nanoparticles, magnetic microparticles andnanoparticles, superparamagnetic microparticles and nanoparticles (e.g.,DYNABEADS® particles, available from Invitrogen Corp., Carlsbad, Calif.,fluorescent microparticles and nanoparticles, coated magneticmicroparticles and nanoparticles, ferromagnetic microparticles andnanoparticles, coated ferromagnetic microparticles and nanoparticles,and those described in U.S. Patent Publication Nos. 20050260686,entitled “Multiplex flow assays preferably with magnetic particles assolid phase,” published on Nov. 24, 2005; 20030132538, entitled“Encapsulation of discrete quanta of fluorescent particles,” publishedon Jul. 17, 2003; 20050118574, entitled “Multiplexed Analysis ofClinical Specimens Apparatus and Method,” published on Jun. 2, 2005;20050277197. Entitled “Microparticles with Multiple Fluorescent Signalsand Methods of Using Same,” published on Dec. 15, 2005; 20060159962,entitled “Magnetic Microspheres for use in Fluorescence-basedApplications,” published on Jul. 20, 2006; the entire disclosures ofwhich are incorporated herein by reference for their teaching concerningbeads and magnetically responsive materials and beads. Beads may bepre-coupled with a biomolecule (ligand). The ligand may, for example, bean antibody, protein or antigen, DNA/RNA probe or any other moleculewith an affinity for the desired target. Examples of droplet actuatortechniques for immobilizing magnetically responsive beads and/ornon-magnetically responsive beads and/or conducting droplet operationsprotocols using beads are described in U.S. patent application Ser. No.11/639,566, entitled “Droplet-Based Particle Sorting,” filed on Dec. 15,2006; U.S. Patent Application No. 61/039,183, entitled “MultiplexingBead Detection in a Single Droplet,” filed on Mar. 25, 2008; U.S. PatentApplication No. 61/047,789, entitled “Droplet Actuator Devices andDroplet Operations Using Beads,” filed on Apr. 25, 2008; U.S. PatentApplication No. 61/086,183, entitled “Droplet Actuator Devices andMethods for Manipulating Beads,” filed on Aug. 5, 2008; InternationalPatent Application No. PCT/US2008/053545, entitled “Droplet ActuatorDevices and Methods Employing Magnetic Beads,” filed on Feb. 11, 2008;International Patent Application No. PCT/US2008/058018, entitled“Bead-based Multiplexed Analytical Methods and Instrumentation,” filedon Mar. 24, 2008; International Patent Application No.PCT/US2008/058047, “Bead Sorting on a Droplet Actuator,” filed on Mar.23, 2008; and International Patent Application No. PCT/US2006/047486,entitled “Droplet-based Biochemistry,” filed on Dec. 11, 2006; theentire disclosures of which are incorporated herein by reference. Beadcharacteristics may be employed in the multiplexing aspects of theinvention. Examples of beads having characteristics suitable formultiplexing, as well as methods of detecting and analyzing signalsemitted from such beads, may be found in U.S. Patent Publication No.20080305481, entitled “Systems and Methods for Multiplex Analysis of PCRin Real Time,” published on Dec. 11, 2008; U.S. Patent Publication No.20080151240, “Methods and Systems for Dynamic Range Expansion,”published on Jun. 26, 2008; U.S. Patent Publication No. 20070207513,entitled “Methods, Products, and Kits for Identifying an Analyte in aSample,” published on Sep. 6, 2007; U.S. Patent Publication No.20070064990, entitled “Methods and Systems for Image Data Processing,”published on Mar. 22, 2007; U.S. Patent Publication No. 20060159962,entitled “Magnetic Microspheres for use in Fluorescence-basedApplications,” published on Jul. 20, 2006; U.S. Patent Publication No.20050277197, entitled “Microparticles with Multiple Fluorescent Signalsand Methods of Using Same,” published on Dec. 15, 2005; and U.S. PatentPublication No. 20050118574, entitled “Multiplexed Analysis of ClinicalSpecimens Apparatus and Method,” published on Jun. 2, 2005.

“Droplet” means a volume of liquid on a droplet actuator. Typically, adroplet is at least partially bounded by filler fluid. For example, adroplet may be completely surrounded by filler fluid or may be boundedby filler fluid and one or more surfaces of the droplet actuator. Asanother example, a droplet may be bounded by filler fluid, one or moresurfaces of the droplet actuator, and the atmosphere. As yet anotherexample, a droplet may be bounded by filler fluid and the atmosphere.Droplets may, for example, be aqueous or non-aqueous or may be mixturesor emulsions including aqueous and non-aqueous components. Droplets maytake a wide variety of shapes; nonlimiting examples include generallydisc shaped, slug shaped, truncated sphere, ellipsoid, spherical,partially compressed sphere, hemispherical, ovoid, cylindrical,combinations of such shapes, and various shapes formed during dropletoperations, such as merging or splitting or formed as a result ofcontact of such shapes with one or more surfaces of a droplet actuator.For examples of droplet fluids that may be subjected to dropletoperations using the approach of the invention, see International PatentApplication No. PCT/US 06/47486, entitled, “Droplet-Based Biochemistry,”filed on Dec. 11, 2006. In various embodiments, a droplet may include abiological sample, such as whole blood, lymphatic fluid, serum, plasma,sweat, tear, saliva, sputum, cerebrospinal fluid, amniotic fluid,seminal fluid, vaginal excretion, serous fluid, synovial fluid,pericardial fluid, peritoneal fluid, pleural fluid, transudates,exudates, cystic fluid, bile, urine, gastric fluid, intestinal fluid,fecal samples, liquids containing single or multiple cells, liquidscontaining organelles, fluidized tissues, fluidized organisms, liquidscontaining multi-celled organisms, biological swabs and biologicalwashes. Moreover, a droplet may include a reagent, such as water,deionized water, saline solutions, acidic solutions, basic solutions,detergent solutions and/or buffers. Other examples of droplet contentsinclude reagents, such as a reagent for a biochemical protocol, such asa nucleic acid amplification protocol, an affinity-based assay protocol,an enzymatic assay protocol, a sequencing protocol, and/or a protocolfor analyses of biological fluids.

“Droplet Actuator” means a device for manipulating droplets. Forexamples of droplet actuators, see Pamula et al., U.S. Pat. No.6,911,132, entitled “Apparatus for Manipulating Droplets byElectrowetting-Based Techniques,” issued on Jun. 28, 2005; Pamula etal., U.S. patent application Ser. No. 11/343,284, entitled “Apparatusesand Methods for Manipulating Droplets on a Printed Circuit Board,” filedon filed on Jan. 30, 2006; Pollack et al., International PatentApplication No. PCT/US2006/1047486, entitled “Droplet-BasedBiochemistry,” filed on Dec. 11, 2006; Shenderov, U.S. Pat. No.6,773,566, entitled “Electrostatic Actuators for Microfluidics andMethods for Using Same,” issued on Aug. 10, 2004 and U.S. Pat. No.6,565,727, entitled “Actuators for Microfluidics Without Moving Parts,”issued on Jan. 24, 2000; Kim et al., U.S. patent application Ser. No.10/343,261, entitled “Electrowetting-driven Micropumping,” filed on Jan.27, 2003; Ser. No. 11/275,668, entitled “Method and Apparatus forPromoting the Complete Transfer of Liquid Drops from a Nozzle,” filed onJan. 23, 2006; Ser. No. 11/460,188, entitled “Small Object Moving onPrinted Circuit Board,” filed on Jan. 23, 2006; Ser. No. 12/465,935,entitled “Method for Using Magnetic Particles in Droplet Microfluidics,”filed on May 14, 2009; Ser. No. 12/513,157, entitled “Method andapparatus for real-time feedback control of electrical manipulation ofdroplets on chip,” filed on Apr. 30, 2009; Velev, U.S. Pat. No.7,547,380, entitled “Droplet Transportation Devices and Methods Having aFluid Surface,” issued on Jun. 16, 2009; Sterling et al., U.S. Pat. No.7,163,612, entitled “Method, Apparatus and Article for MicrofluidicControl via Electrowetting, for Chemical, Biochemical and BiologicalAssays and the Like,” issued on Jan. 16, 2007; Becker and Gascoyne etal., U.S. Pat. No. 7,641,779, entitled “Method and Apparatus forProgrammable fluidic Processing,” issued on Jan. 5, 2010, and U.S. Pat.No. 6,977,033, entitled “Method and Apparatus for Programmable fluidicProcessing,” issued on Dec. 20, 2005; Decre et al., U.S. Pat. No.7,328,979, entitled “System for Manipulation of a Body of Fluid,” issuedon Feb. 12, 2008; Yamakawa et al., U.S. Patent Pub. No. 20060039823,entitled “Chemical Analysis Apparatus,” published on Feb. 23, 2006; Wu,International Patent Pub. No. WO/2009/003184, entitled “DigitalMicrofluidics Based Apparatus for Heat-exchanging Chemical Processes,”published on Dec. 31, 2008; Fouillet et al., U.S. Patent Pub. No.20090192044, entitled “Electrode Addressing Method,” published on Jul.30, 2009; Fouillet et al., U.S. Pat. No. 7,052,244, entitled “Device forDisplacement of Small Liquid Volumes Along a Micro-catenary Line byElectrostatic Forces,” issued on May 30, 2006; Marchand et al., U.S.Patent Pub. No. 20080124252, entitled “Droplet Microreactor,” publishedon May 29, 2008; Adachi et al., US. Patent Pub. No. 20090321262,entitled “Liquid Transfer Device,” published on Dec. 31, 2009; Roux etal., U.S. Patent Pub. No. 20050179746, entitled “Device for Controllingthe Displacement of a Drop Between two or Several Solid Substrates,”published on Aug. 18, 2005; Dhindsa et al., “Virtual ElectrowettingChannels: Electronic Liquid Transport with Continuous ChannelFunctionality,” Lab Chip, 10:832-836 (2010); the disclosures of whichare incorporated herein by reference, along with their prioritydocuments. Certain droplet actuators will include a base substrate,droplet operations electrodes associated with the substrate, one or moredielectric and/or hydrophobic layers atop the substrate and/orelectrodes forming a droplet operations surface, and optionally, a topsubstrate separated from the droplet operations surface by a gap. Thebase and top substrates may in some cases be formed as one integralcomponent. One or more reference electrodes may be provided on the topand/or bottom substrates and/or in the gap. In various embodiments, themanipulation of droplets by a droplet actuator may be electrodemediated, e.g., electrowetting mediated or dielectrophoresis mediated orCoulombic force mediated. Examples of other methods of controlling fluidflow that may be used in the droplet actuators of the invention includedevices that induce hydrodynamic fluidic pressure, such as those thatoperate on the basis of mechanical principles (e.g., external syringepumps, pneumatic membrane pumps, vibrating membrane pumps, vacuumdevices, centrifugal forces, piezoelectric/ultrasonic pumps and acousticforces); electrical or magnetic principles (e.g., electroosmotic flow,electrokinetic pumps, ferrofluidic plugs, electrohydrodynamic pumps,attraction or repulsion using magnetic forces and magnetohydrodynamicpumps); thermodynamic principles (e.g., gas bubblegeneration/phase-change-induced volume expansion); other kinds ofsurface-wetting principles (e.g., electrowetting, andoptoelectrowetting, as well as chemically, thermally, structurally andradioactively induced surface-tension gradients); gravity; surfacetension (e.g., capillary action); electrostatic forces (e.g.,electroosmotic flow); centrifugal flow (substrate disposed on a compactdisc and rotated); magnetic forces (e.g., oscillating ions causes flow);magnetohydrodynamic forces; and vacuum or pressure differential. Incertain embodiments, combinations of two or more of the foregoingtechniques may be employed in droplet actuators of the invention.

“Droplet operation” means any manipulation of a droplet on a dropletactuator. A droplet operation may, for example, include: loading adroplet into the droplet actuator; dispensing one or more droplets froma source droplet; splitting, separating or dividing a droplet into twoor more droplets; transporting a droplet from one location to another inany direction; merging or combining two or more droplets into a singledroplet; diluting a droplet; mixing a droplet; agitating a droplet;deforming a droplet; retaining a droplet in position; incubating adroplet; heating a droplet; vaporizing a droplet; cooling a droplet;disposing of a droplet; transporting a droplet out of a dropletactuator; other droplet operations described herein; and/or anycombination of the foregoing. The terms “merge,” “merging,” “combine,”“combining” and the like are used to describe the creation of onedroplet from two or more droplets. It should be understood that whensuch a term is used in reference to two or more droplets, anycombination of droplet operations that are sufficient to result in thecombination of the two or more droplets into one droplet may be used.For example, “merging droplet A with droplet B,” can be achieved bytransporting droplet A into contact with a stationary droplet B,transporting droplet B into contact with a stationary droplet A, ortransporting droplets A and B into contact with each other. The terms“splitting,” “separating” and “dividing” are not intended to imply anyparticular outcome with respect to volume of the resulting droplets(e.g., the volume of the resulting droplets can be the same ordifferent) or number of resulting droplets (the number of resultingdroplets may be 2, 3, 4, 5 or more). The term “mixing” refers to dropletoperations which result in more homogenous distribution of one or morecomponents within a droplet. Examples of “loading” droplet operationsinclude microdialysis loading, pressure assisted loading, roboticloading, passive loading, and pipette loading. Droplet operations may beelectrode-mediated. In some cases, droplet operations are furtherfacilitated by the use of hydrophilic and/or hydrophobic regions onsurfaces and/or by physical obstacles. For examples of dropletoperations, see the patents and patent applications cited above underthe definition of “droplet actuator.”

“Filler fluid” means a fluid associated with a droplet operationssubstrate of a droplet actuator, which fluid is sufficiently immisciblewith a droplet phase to render the droplet phase subject toelectrode-mediated droplet operations. The filler fluid may, forexample, be a low-viscosity oil, such as silicone oil. Other examples offiller fluids are provided in International Patent Application No.PCT/US2006/047486, entitled, “Droplet-Based Biochemistry,” filed on Dec.11, 2006; International Patent Application No. PCT/US2008/072604,entitled “Use of additives for enhancing droplet actuation,” filed onAug. 8, 2008; and U.S. Patent Publication No. 20080283414, entitled“Electrowetting Devices,” filed on May 17, 2007; the entire disclosuresof which are incorporated herein by reference. The filler fluid may fillthe entire gap of the droplet actuator or may coat one or more surfacesof the droplet actuator. Filler fluid may be conductive ornon-conductive.

“Immobilize” with respect to magnetically responsive beads, means thatthe beads are substantially restrained in position in a droplet or infiller fluid on a droplet actuator. For example, in one embodiment,immobilized beads are sufficiently restrained in position to permitexecution of a splitting operation on a droplet, yielding one dropletwith substantially all of the beads and one droplet substantiallylacking in the beads.

“Magnetically responsive” means responsive to a magnetic field.“Magnetically responsive beads” include or are composed of magneticallyresponsive materials. Examples of magnetically responsive materialsinclude paramagnetic materials, ferromagnetic materials, ferrimagneticmaterials, and metamagnetic materials. Examples of suitable paramagneticmaterials include iron, nickel, and cobalt, as well as metal oxides,such as Fe₃O₄, BaFe₁₂O₁₉, CoONiO, Mn₂O₃, Cr₂O₃, and CoMnP.

“Transporting into the magnetic field of a magnet,” “transportingtowards a magnet,” and the like, as used herein to refer to dropletsand/or magnetically responsive beads within droplets, is intended torefer to transporting into a region of a magnetic field capable ofsubstantially attracting magnetically responsive beads in the droplet.Similarly, “transporting away from a magnet or magnetic field,”“transporting out of the magnetic field of a magnet,” and the like, asused herein to refer to droplets and/or magnetically responsive beadswithin droplets, is intended to refer to transporting away from a regionof a magnetic field capable of substantially attracting magneticallyresponsive beads in the droplet, whether or not the droplet ormagnetically responsive beads is completely removed from the magneticfield. It will be appreciated that in any of such cases describedherein, the droplet may be transported towards or away from the desiredregion of the magnetic field, and/or the desired region of the magneticfield may be moved towards or away from the droplet. Reference to anelectrode, a droplet, or magnetically responsive beads being “within” or“in” a magnetic field, or the like, is intended to describe a situationin which the electrode is situated in a manner which permits theelectrode to transport a droplet into and/or away from a desired regionof a magnetic field, or the droplet or magnetically responsive beadsis/are situated in a desired region of the magnetic field, in each casewhere the magnetic field in the desired region is capable ofsubstantially attracting any magnetically responsive beads in thedroplet. Similarly, reference to an electrode, a droplet, ormagnetically responsive beads being “outside of” or “away from” amagnetic field, and the like, is intended to describe a situation inwhich the electrode is situated in a manner which permits the electrodeto transport a droplet away from a certain region of a magnetic field,or the droplet or magnetically responsive beads is/are situated in awayfrom a certain region of the magnetic field, in each case where themagnetic field in such region is not capable of substantially attractingany magnetically responsive beads in the droplet.

“Washing” with respect to washing a bead means reducing the amountand/or concentration of one or more substances in contact with the beador exposed to the bead from a droplet in contact with the bead. Thereduction in the amount and/or concentration of the substance may bepartial, substantially complete, or even complete. The substance may beany of a wide variety of substances; examples include target substancesfor further analysis, and unwanted substances, such as components of asample, contaminants, and/or excess reagent. In some embodiments, awashing operation begins with a starting droplet in contact with amagnetically responsive bead, where the droplet includes an initialamount and initial concentration of a substance. The washing operationmay proceed using a variety of droplet operations. The washing operationmay yield a droplet including the magnetically responsive bead, wherethe droplet has a total amount and/or concentration of the substancewhich is less than the initial amount and/or concentration of thesubstance. Examples of suitable washing techniques are described inPamula et al., U.S. Pat. No. 7,439,014, entitled “Droplet-Based SurfaceModification and Washing,” granted on Oct. 21, 2008, the entiredisclosure of which is incorporated herein by reference.

The terms “top,” “bottom,” “over,” “under,” and “on” are used throughoutthe description with reference to the relative positions of componentsof the droplet actuator, such as relative positions of top and bottomsubstrates of the droplet actuator. It will be appreciated that thedroplet actuator is functional regardless of its orientation in space.

When a liquid in any form (e.g., a droplet or a continuous body, whethermoving or stationary) is described as being “on”, “at”, or “over” anelectrode, array, matrix or surface, such liquid could be either indirect contact with the electrode/array/matrix/surface, or could be incontact with one or more layers or films that are interposed between theliquid and the electrode/array/matrix/surface.

When a droplet is described as being “on” or “loaded on” a dropletactuator, it should be understood that the droplet is arranged on thedroplet actuator in a manner which facilitates using the dropletactuator to conduct one or more droplet operations on the droplet, thedroplet is arranged on the droplet actuator in a manner whichfacilitates sensing of a property of or a signal from the droplet,and/or the droplet has been subjected to a droplet operation on thedroplet actuator.

6 BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a side view and a top view, respectively, ofa droplet actuator configured for sample-to-result analysis of a singlebiological sample;

FIGS. 2A through 2C illustrate side views and a top view of anotherexample of a droplet actuator configured for sample-to-result analysisof a single biological sample;

FIG. 3 illustrates a portion of the droplet actuator of FIG. 2 andillustrates the arrangement of a physical barrier for separating ablister pack compartment from an opening in the top substrate;

FIGS. 4A and 4B illustrate a top view and a cross-sectional view,respectively, of a droplet actuator and illustrate variations in gapheight associated with certain droplet operation regions;

FIGS. 5A, 5B, and 5C illustrate other top views of the droplet actuatorof FIGS. 4A and 4B and show a process of concentrating and dispensingmagnetically responsive beads from a large sample volume;

FIGS. 6A and 6B illustrate a top view and a side view, respectively, ofa droplet actuator and illustrate variations in gap height associatedwith sample storage and waste disposal regions;

FIGS. 7A and 7B illustrate another top view and side view, respectively,of the droplet actuator of FIGS. 4A and 4B and illustrate anotherexample of a two-step droplet actuator configured for integratedsample-to-result analysis of a single biological sample;

FIG. 8 illustrates yet another side view of a portion of the dropletactuator of FIGS. 4A and 4B and illustrates the interface betweendroplet operations and waste disposal regions where the gap heighttransitions from H1 to H2;

FIGS. 9A and 9B illustrate yet another top view and side view,respectively, of the droplet actuator of FIGS. 4A and 4B and illustratean example of a three-step droplet actuator configured for integratedsample-to-result analysis of a single biological sample;

FIG. 10 illustrates yet another top view of the droplet actuator ofFIGS. 4A and 4B and illustrates an example of suitable dimensions ofcertain droplet operations regions on a droplet actuator;

FIGS. 11A through 11C illustrate top views of an electrode arrangementand show a process for mixing a small volume of fluid with a largervolume of fluid;

FIGS. 12A and 12B illustrate top views of an electrode arrangement andshow another process for mixing a larger volume of fluid;

FIG. 13 illustrates a side view of an example of an on-actuator samplereservoir of a droplet actuator and illustrates a method of mixing largevolumes of liquid with smaller volumes of reagents;

FIG. 14 illustrates a side view of an example of a portion of a dropletactuator and illustrates another method of mixing a larger volume offluid with a smaller volume of fluid;

FIG. 15 illustrates a side view of a portion of a droplet actuator andillustrates another method of mixing a large volume of fluid in adroplet actuator;

FIGS. 16A and 16B illustrate yet other top views of the droplet actuatorof FIGS. 4A and 4B and illustrate the arrangement of one or more magnetsthat may be used to concentrate and collect a quantity of magneticallyresponsive beads from a large sample volume;

FIG. 17 illustrates a side view of a portion of a droplet actuator thatincludes a strong magnet positioned a certain distance away from thebottom surface of the droplet actuator;

FIGS. 18A through 18C illustrate top views of an electrode arrangementof a portion of a droplet actuator and illustrate a process oftransporting a small droplet onto a reservoir electrode;

FIGS. 19A through 19D illustrate side views of a portion of a dropletactuator and illustrate methods for containing the sample space of anon-actuator reservoir;

FIGS. 20A and 20B illustrate perspective views of two exampleembodiments of a detection system for detection of multiple (e.g., four)different fluorophores at a single detection spot;

FIG. 21 illustrates a top view of an example of a portion of a dropletactuator and illustrates methods for controlling the flow of heat incertain regions (temperature control zones) of a droplet actuator;

FIGS. 22A, 22B, and 22C illustrate top views of an example of a portionof a droplet actuator and illustrate methods for co-locating temperaturecontrol zones and associated heat spreaders on a droplet actuator;

FIG. 23A illustrates a top view of an example of a portion of a dropletactuator and illustrate a method for forming a temperature gradientalong a path of droplet operations electrodes;

FIG. 23B illustrates a top view of an example of a portion of a dropletactuator that includes an arrangement of multiple heat spreaders of FIG.23A;

FIG. 24 illustrates a top view of an example of a portion of a dropletactuator and illustrates another method for forming a temperaturegradient along a path of droplet operations electrodes;

FIG. 25 illustrates a perspective view of a resistive heating devicethat includes resistive heaters mounted to spring-loaded metallicconductors;

FIG. 26 illustrate a perspective view of another example of a heatingdevice, wherein the heating device includes one or more flex heaterassemblies;

FIGS. 27A and 27B illustrate side views of an example of a portion of anelectrowetting effector board configured for generation of resistiveheat and illustrate the alignment of the effector board with amicrofluidic chip for resistive heat transfer;

FIG. 28 illustrates a side view of an example of a portion of a dropletactuator that is configured for radiative heat transfer to a temperaturecontrol zone on a droplet actuator;

FIG. 29A illustrates an example of a portion of a droplet actuator forcontrolling the temperature of a droplet by position dithering;

FIG. 29B illustrates a schematic diagram of an example of a thermalcircuit for the droplet actuator of FIG. 29A that is configured forposition dithering; and

FIG. 29C illustrates a schematic view of an example of an electricalequivalent circuit for position dithering used for droplet temperaturecontrol on the droplet actuator of FIG. 29A.

7 DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a droplet actuator device and methods forintegrated sample preparation and analysis of a liquid sample, such as abiological sample. The droplet actuator device and methods of theinvention perform sample preparation and analysis from a single sampleon the same droplet actuator. The droplet actuator device uses a largeinput sample volume (e.g., about 1 milliliter (mL)) and provides forrapid capture and concentration of target analytes for subsequentmolecular diagnostic assays (e.g., qPCR, immunoassay).

In one embodiment, the droplet actuator device and methods of theinvention provide for increased droplet throughput for rapid samplepreparation and analysis. In one example, increased droplet throughputis provided by manipulation of larger sized droplets.

In another embodiment, the droplet actuator device and methods of theinvention provide for efficient and controllable loading (e.g., reliableloading) of a large sample volume (e.g., about 1 mL) into a dropletactuator. In one example, reliable loading is provided by loading thesample in an on-actuator reservoir (on-actuator meaning in the dropletoperations gap or on the droplet operations surface). In one embodiment,the reservoir into which the sample is loaded is in the dropletoperations gap, and is specifically not a reservoir outside the dropletoperations gap, such as a reservoir situated in the top substrate.

In another embodiment, the droplet actuator device and methods of theinvention provide for effective mixing of analyte capture beads within asample. In one example, electrowetting may be used to mix a samplestored in an on-actuator reservoir, e.g., by shuttling the droplet backand forth within the on-actuator reservoir.

In another embodiment, the droplet actuator device and methods of theinvention provide for rapid and efficient concentration and collectionof analyte capture beads, e.g., magnetically responsive capture beads.One or more magnets may be arranged in proximity of a sample stored inan on-actuator reservoir. The magnet may, for example, be stationary ormoveable, permanent or electrically controllable, or any combination ofthe foregoing.

In yet another embodiment, the invention provides a detection systemthat uses a single excitation beam and a single detection beam tocollect multiple (e.g., four) different fluorescent signals at a singledetection spot on a droplet actuator.

In yet another embodiment, the invention provides methods forcontrolling heat distribution within a droplet operations gap.Similarly, the invention provides methods for controlling heatdistribution within a filler fluid in a droplet operations gap.Similarly, the invention provides methods for controlling heatdistribution within an oil filler fluid, such as low viscosity oil, suchas silicone oil, in a droplet operations gap. The methods may minimizethermal losses in one or more temperature control zones on a dropletactuator. The thermal control aspect of the invention permits heat to begenerated off-actuator (exterior to the droplet operations gap and offof the droplet operations surface), and transferred to designatedtemperature control zones on a droplet actuator. In yet anotherembodiment, the invention provides methods for controlling thetemperature of a droplet by transporting the droplet from onetemperature region to another temperature region (position dithering) ona droplet actuator.

7.1 Droplet Actuator Devices

FIGS. 1A and 1B illustrate a side view and a top view, respectively, ofa droplet actuator 100 configured for sample-to-result analysis of asingle biological sample. In one embodiment, droplet actuator 100 isconfigured for integrated sample preparation and PCR analysis of asingle sample for the presence and/or quantity of a nucleic acidanalyte. In another embodiment, droplet actuator 100 is configured forintegrated sample preparation and immunoassay analysis of a singlesample.

Droplet actuator 100 may include a bottom substrate 110 and a topsubstrate 112 that are separated by a gap 114. A gasket 116 may be usedto provide a seal around the outer edge of droplet actuator 100. Gasket116 (as well as other gaskets described herein) may, for example, beformed of a polymeric substance, such as a polymeric gasket material,and/or an adhesive. Examples of suitable adhesives include UV curableadhesives such as PERMABOND® UV648 and UV648, MASTERBOND® 15x-5, and 3M®transfer tapes, such as 3M VHB 3905 and 3M 300 LSE. Bottom substrate 110may include an arrangement of droplet operations electrodes 118 (e.g.,electrowetting electrodes). Droplet operations are conducted atopdroplet operations electrodes 118 on a droplet operations surface.

Top substrate 112 may, for example, be formed of a molded material, suchinjection-molded plastic, or from multiple materials, such as glasscombined with injection molded plastic. One or more reservoirs 120,e.g., reservoirs 120 a and 120 b and a sample input reservoir 122, maybe provided. Reservoirs 120 may be integrated into top substrate 112 andmay be coupled to a path arranged for flowing fluid into the dropletoperations gap. One or more openings 124, e.g., openings 124 a through124 d, are provided within top substrate 112. Openings 124 establish afluid path from reservoirs 120 and sample input reservoir 122 intosufficient proximity of certain droplet operations electrodes 118 onbottom substrate 110. Openings 124 may be closed with a breachable seal126, e.g., breachable seals 126 a through 126 c. Breachable seals 126may, for example, be formed of a wax material that may be breached bythe application of a sufficient amount of heat to melt the wax.Breachable seals may alternatively be physically removed or breached,such as by puncturing. For example, an awl (not shown) may be providedfor puncturing or removing breachable seals 126. Sample input reservoir122 includes a vent opening 128 for venting air as liquid is introducedinto gap 114. A hinged cap 130 may be used to close sample inputreservoir 122 and vent opening 128. Top substrate 112 may also include arecessed area 132. In operation, recessed area 132 may be used tofacilitate arrangement of a detector in proximity to the dropletoperations gap for detection of reaction products.

Droplet actuator 100 may include one or more temperature control zones134, e.g., temperature control zones 134 a through 134 c, for performingcertain process steps at predetermined temperatures. One or more heaterbars 136, e.g., heater bars 136 a through 136 c, may be used to melt thewax seals (e.g., breachable seals 126) and/or to control the temperatureof filler fluid that is in gap 114 to establish temperature controlzones 134. In one example, temperature control zone 134 a may be usedfor sample preparation and denaturation of DNA for PCR analysis. In thisexample, heater bar 136 a may be used to heat temperature control zone134 a to a temperature suitable for denaturation of sample DNA. Heaterbars 136 b and 136 c may be used to heat temperature control zones 134 band 134 c to temperatures affective to conduct other reaction steps,such as annealing of primer to single-stranded DNA template and primerextension by DNA polymerase. By cycling a droplet includingamplification reagents and a sample including a target nucleic acidthrough the thermal zones, the target nucleic acid may be amplified.Real-time detection may be used to detect amplified product duringamplification and/or an end-point measurement may be taken.

A magnet 138 may be associated with droplet actuator 100. Magnet 138 maybe arranged such that sample input reservoir 122 is within the magneticfield of magnet 138. Magnet 138 may, for example, be a permanent magnetor an electromagnet. Magnet 138 may be used, for example, to attractand/or immobilize a quantity of magnetically responsive capture beads(not shown). In operation, magnet 138 may be used to assist in a processof a concentrating and collecting target nucleic acid captured onmagnetic beads from a sample fluid for PCR analysis. Magnet 138 may beused to assist in a process of removing unwanted materials from a sampleprior to analysis. Heater 140 may be associated with droplet actuator100. Heater 140 may, for example, be an ultrasonic heater, which forsupplying sound and thermal energy (e.g., ultrasound) to a sample fluidto agitate and/or disrupt particles (e.g., to perform cell lysis) in thefluid.

Referring to FIG. 1B, the arrangement of droplet operations electrodes118 may include multiple dispensing electrodes, such as, but not limitedto, sample dispensing electrodes 142 a and 142 b for dispensing samplefluids (e.g., DNA immobilized on magnetically responsive beads); reagentdispensing electrodes 144 a and 144 b for dispensing sample preparationreagent fluids, such as wash buffer and DNA elution buffer: and reagentdispensing electrodes 146 a and 146 b for dispensing PCR reagent fluids,such as dNTPs and enzyme. Sample dispensing electrodes 142, reagentdispensing electrodes 144 and 146 are interconnected through anarrangement, such as a path or array, of droplet operations electrodes118. A detection spot 148 is positioned in proximity of recessed area132, for example for detecting target components from or of a sample.

Sample preparation reagents and assay reagents (e.g., PCR reagents) maybe pre-loaded and stored on droplet actuator 100. Pre-loading of dropletactuator 100 with assay components provides a ready-to-use device thatminimizes hands-on time during operation. In one example, a quantity ofdried sample preparation reagents 150 (e.g., magnetically responsivebeads) may be deposited and stored in sample input reservoir 122. Aquantity of dried PCR reagents 152 may be deposited and stored inreservoir 120 a within openings 126 a and 126 b. A quantity ofreconstitution buffer 154 may be deposited and stored in reservoir 120a. A quantity of filler fluid 156 (e.g., silicone oil) may be depositedand stored in reservoir 120 b. Filler fluid 156 is of sufficientquantity to fill gap 114 during operation of droplet actuator 100.

FIGS. 2A through 2C illustrate side views and a top view of anotherexample of a droplet actuator 200 that is configured forsample-to-result analysis of a single biological sample. Dropletactuator 200 is an example of a droplet actuator in which filler fluid,sample preparation reagents, and assay reagents (e.g. PCR reagents) arepre-loaded. One or more of the filler fluid, buffers and reagents may beprovided in a reagent storage substrate, which may take the form of a“blister pack.” The reagent storage substrate is made of a deformablematerial and includes cavities or pockets suitable for storing liquid ordried reagents. Preferably a material is selected which does notinteract with the buffers or reagents to an extent that renders themunsuited for their intended use. Examples of suitable materials for thereagent storage layer include polyvinyl chloride (PVC),polychlorotrifluoroethylene (PCTFE), and cyclic olefin copolymers (COC).

Droplet actuator 200 may include a bottom substrate 210 and a topsubstrate 212 that are separated by a gap 214. A gasket 216 may be usedto provide a seal around the outer edge of gap 214. Bottom substrate 210and/or top substrate 212 may include an arrangement of dropletoperations electrodes 218 (e.g., electrowetting electrodes). Dropletoperations are controlled by droplet operations electrodes 218 on adroplet operations surface.

Top substrate 212 may, for example, be formed of injection-moldedplastic. An area of increased gap height may be provided in the dropletoperations gap to establish an on-actuator sample reservoir 220(on-actuator meaning in the droplet operations gap or on the dropletoperations surface). An off-actuator sample input reservoir 222 (offactuator meaning exterior to the droplet operations gap and off of thedroplet operations surface), may be positioned relative to in-gap samplereservoir 220 and arranged with one or more fluid paths to flow liquidfrom off actuator reservoir 222 into on actuator reservoir 220. Areagent storage layer 224 may be provided atop top substrate 212.Reagent storage layer 224 may, for example, be formed of plastic, oranother suitable material. Reagent storage layer 224 may include one ormore compartments 226, e.g., compartments 226 a through 226 d, in ablister pack array. Sample input reservoir 222 and compartments 226 maycontain (e.g., pre-loaded) a quantity of fluids or dried reagents. Inone example, sample input reservoir 222 may contain a quantity of driedreagents 228. Compartment 226 a may include a quantity of filler fluid230 such as silicone oil. Compartments 226 b and 226 d may include aquantity of dried reagents 232, such as PCR or immunoassay reagents.Compartment 226 c may contain a quantity of reagent reconstitutionbuffer 234. Filler fluid 230 and reconstitution buffer 234 containedwithin compartments 226 are physically separated from dried reagents 232and/or gap 214 by one or more frangible seals within the blister packarray as described in more detail with reference to FIG. 3.

One or more openings 236, e.g., openings 236 a through 236 d, areprovided within top substrate 212. Openings 236 establish a fluid pathfrom reagent storage layer 224 and sample input reservoir 222 intoproximity with droplet operations electrodes 218 on bottom substrate 210(that is, proximity which is sufficient to permit the droplets to becontrolled by the electrodes). Openings 236 may be closed with abreachable seal 238, e.g., breachable seals 238 a through 238 c.Breachable seals 238 may, for example be formed of a wax material thatmay be removed by the application of a sufficient amount of heat to meltthe wax. Sample input reservoir 222 includes a vent opening 240 forventing air as liquid is introduced into gap 214. A cap 242, such as ahinged cap, may be used to close sample input reservoir 222 and ventopening 240. In another embodiment, sample input reservoir 222 mayfunction as a venting port and vent opening 240 may be eliminated.

One or more heater bars 244, e.g., heater bars 244 a through 244 d, maybe associated with droplet actuator 200. Heater bars 244 may be used tomelt the wax seals (e.g., breachable seals 238) and/or control thetemperature of filler fluid in vicinity of heater bars 244, e.g., asdescribed above with respect to FIGS. 1A and 1B.

A magnet 246 may be associated with droplet actuator 200. Magnet 246may, for example, be a permanent magnet or an electromagnet. Magnet 246may, for example, be used to attract and/or immobilize a quantity ofmagnetically responsive capture beads (not shown). In operation, magnet246 may be used with magnetic beads to assist in a process of aconcentrating and collecting target nucleic acid from a sample fluid forPCR analysis, collecting other analytes, or removing unwantedcomponents, e.g., as described above with respect to FIGS. 1A and 1B.

A sonicator 248 may be associated with droplet actuator 200. Thesonicator may be any source of sonic energy and may be provided as acomponent of the droplet actuator cartridge or as a component of aninstrument or cartridge docking station, modular drive or bay to whichthe droplet actuator cartridge is coupled during operation (e.g., asdescribed in Pollack et al., U.S. Patent Pub. No. 20100143963, entitled“Modular Droplet Actuator Drive,” published on Jun. 10, 2010, the entiredisclosure of which is incorporated herein by reference). Referring toFIG. 2A, in one embodiment, sonicator 248 may be in contact withoff-actuator (meaning outside the droplet operations gap) sample inputreservoir 222. Referring to FIG. 2B, in another embodiment, sonicator248 may be in contact with top substrate 212 near on-actuator sampleinput reservoir 222. Sonicator 248 may be used to apply sound energy(e.g., ultrasound) to a sample fluid to agitate and/or disrupt particles(e.g., to perform cell lysis) in the fluid. Referring to FIG. 2C, thearrangement of droplet operations electrodes 218 may include multipledispensing electrodes, such as, but not limited to, sample dispensingelectrodes 250 a and 250 b for dispensing sample fluids (e.g., DNAimmobilized on magnetically responsive beads); reagent dispensingelectrodes 252 a and 252 b for dispensing sample preparation reagentfluids, such as wash buffer and DNA elution buffer; and reagentdispensing electrodes 254 a and 254 b for dispensing PCR reagent fluids,such as dNTPs and enzyme. Sample dispensing electrodes 250, reagentdispensing electrodes 252 and 254 are interconnected through anarrangement, such as a path or array, of droplet operations electrodes218. The arrangement of droplet operations electrodes 218 and positionof heater bars 244 provide certain droplet operations regions 256, e.g.,droplet operations regions 256 a through 256 c, for performing differentprocessing steps. A detection spot 258 is positioned within dropletoperations regions 256 c.

Droplet actuator 200 may be manufactured by loading reagents and/orreconstitution solutions into compartments 226. An adhesive may bepatterned onto a top surface of top substrate 212 and/or on reagentstorage layer 226. Reagent storage layer 226 may be affixed to a topsurface of top substrate 212, thereby sealing reagents andreconstitution solutions. Like other droplet actuator embodiments of theinvention, droplet actuator 200 may be labeled and packaged. Dropletactuator 200 may be packaged together with other components, such asinstructions for use of droplet actuator 200. In some cases, openings236 may be sealed by the reagent storage layer, e.g., as shown withrespect to opening 236 a (see also FIG. 3).

In operation, a volume of sample fluid is loaded into sample inputreservoir 222 and hinged cap 232 is closed. The sample fluid may, forexample, be a blood sample or a nasal pharyngeal wash sample of about 1ml or more in volume that contains a quantity of target analytes (e.g.,bacterial, viral, and/or fungal targets), or other biological sample. Asthe sample fluid is loaded into sample input reservoir 222, samplepreparation reagents 228 are reconstituted. The frangible sealsenclosing compartments 226 a and 226 c are disrupted by the applicationof pressure (e.g., closing the lid of the instrument) such that fillerfluid 230, e.g., silicone oil, is released into gap 214 andreconstitution buffer 234 is released into adjacent compartments 226 band 226 d or manually pressing the compartments to force flow of thereconstitution buffer into contact with the dried reagents and into thedroplet operations gap. As reconstitution buffer is released into theadjacent compartments, dried reagents 232 are reconstituted. Whenpresent, sonicator 240 may be activated and used to agitate particlesand/or lyse cells (disrupt cell membranes) in the sample fluid. Asonicator may also or alternatively be provided to acceleratereconstitution of dried reagents. Where wax seals are present, heaterbar 244 a is heated to a temperature that is sufficient to melt wax seal238 c. As wax seal 238 c is melted, the lysed sample fluid is releasedinto on-actuator sample reservoir 220 for further processing. In anotherexample, referring to FIG. 2B, the sample fluid is first released intoon-actuator sample reservoir 220 and subsequently lysed by activation ofsonicator 240. In another embodiment,

FIG. 3 illustrates a portion of droplet actuator 200 of FIG. 2 andillustrates the arrangement of a physical barrier for separating ablister pack compartment from an opening in the top substrate. Forexample, compartment 226, a component of reagent storage layer 224, withfiller fluid 230 therein is physically separated from opening 236 a by aphysical barrier 310. Physical barrier 310 may, for example, be afrangible barrier, such as a pressure sensitive seal, such as anadhesive selected to permit the seal to be broken upon application ofpressure to compartment. Because physical barrier 310 is frangible,e.g., a pressure sensitive seal, a certain amount of pressure may beapplied on physical barrier 310 in order to break the seal and releasefiller fluid 230 from compartment 226 a into opening 236 a and into thegap of the droplet actuator. A single frangible seal separating ablister pack compartment from an opening in the top substrate isillustrated in FIG. 3, but any number of frangible seals may be used toseparate any liquid contained in a blister pack compartment from the gapin a droplet actuator and/or other liquids or dried reagents in adjacentblister pack compartments. The arrangement of physical barriers 310 andremovable wax seals (referring to FIGS. 2A and 2B) provide forcompartmentalization of reagents until the droplet actuator is loadedinto an instrument deck and ready for use. Adhesives may be patterned onthe reagent storage layer 224 or top substrate 212 in a manner whichpermits barrier 310 to be breached upon application of pressure tocompartment 226 a, but without breaching other sealed portions ofreagent storage layer 224 which are not intended to be broken.

FIGS. 4A and 4B illustrate a droplet actuator 400 and illustratevariations in gap height associated with certain droplet operationregions. FIG. 4A illustrates a top view of droplet actuator 400. FIG. 4Billustrates a cross-sectional view of droplet actuator 400 taken alongline A-A of FIG. 4A. Droplet actuator 400 is an example of a two-stepdroplet actuator that is configured for manipulation of different sizedroplets, e.g., from about 1000 μL to about 2.5 in a sample-to-resultprotocol.

Droplet actuator 400 may include a bottom substrate 410 and a topsubstrate 412 that are separated by a gap 414. The region of gap 414essentially serves as an on actuator reservoir with capabilities foraccepting and mixing reagents via an opening in top substrate 412. Agasket 416 may be used to provide a seal around the outer edge ofdroplet actuator 400. Bottom substrate 410 may include an arrangement ofdroplet operations electrodes 418 (e.g., electrowetting electrodes).Droplet operations are conducted atop droplet operations electrodes 418on a droplet operations surface. Droplet actuator 400 may includecertain regions for performing certain process steps. For example,droplet actuator 400 may include, but is not limited to, a sampledispensing region 420 (e.g., storage and dispensing) and a dropletoperations region 422 (e.g., mixing, incubation, washing, detection).Additionally, the height of gap 414 at each region may vary. Dropletactuator 400 of the invention is not limited to the number, types, andphysical arrangement of regions that are shown in FIGS. 4A and 4B. Theconfiguration of droplet actuator 400 that is shown in FIGS. 4A and 4Bis exemplary only. Any number, types, and physical arrangement ofregions having the same and/or different gap heights in a dropletactuator is possible. Other examples are described in reference to FIGS.6 through 9B.

One or more sample dispensing electrodes 424, e.g., sample dispensingelectrodes 424 a through 424 e, and reagent dispensing electrodes 426,e.g., reagent dispensing electrodes 426 a through 426 d, may be arrangedin relation to droplet operations electrodes 418. Sample dispensingelectrodes 424 may, for example, be used to manipulate a large volume ofsample fluid (e.g., about 1 mL) that contains a quantity of magneticallyresponsive beads for processing within droplet actuator 400. To providefor manipulating a large volume of sample fluid, sample dispensingelectrodes 424 c, 424 d, and 424 e may, for example, be installed on apitch of about 2.25 mm. In one embodiment, the region of increased gapheight is associated with path of adjacent electrodes, such as sampledispensing electrodes 424 c, 424 d, and 424 e, which are, relative tothe direction of dispensing, wider than they are long, as shown in FIG.4A. Reagent dispensing electrodes 426 may, for example be used todispense one or more reagent droplets, such as wash buffer droplets,elution buffer droplets, and PCR reagent droplets, for combining with asample droplet for PCR analysis of target nucleic acid sequences, or forshuttling a droplet back and forth for mixing. One or more wastedisposal electrodes 428, e.g., waste disposal electrodes 428 a through428 d, may be may be positioned within a waste disposal region (notshown in FIG. 4B cross-section). Sample dispensing electrodes 626 andwaste disposal electrodes 428 are interconnected by a path or array ofdroplet operations electrodes 418. The interface between dropletoperations region 422 and a waste disposal region, where the gap heighttransitions from H1 to H2, is described in more detail with reference toFIG. 6 and FIG. 8. In one embodiment, the height transition region fromH1 to H2 is aligned with an edge of an electrode, e.g., as shown inFIGS. 4A and 4B. In an alternative embodiment (not shown), an electrode,such as electrode 424 b, spans the height transition region from H1 toH2.

The configuration of droplet actuator 400 is such that a single droplet(not shown) may be dispensed, using a typical electrowetting dispensingelectrode activation scheme, from sample dispensing electrodes 424 ontodroplet operations electrodes 418 for transport and processing withindroplet actuator 400. The variability in gap height that may beassociated with different processing regions (e.g., sample dispensingregion 420 and droplet operations region 422) in droplet actuator 400 isillustrated in FIG. 4B. In this example, two different gap heights alonggap 414 may be associated with the different processing regions. Sampledispensing region 420 of droplet actuator 400 may have a certain gapheight (H2) that is sufficiently large (e.g., >3 mm) to facilitatestorage of larger liquid volumes (e.g., about 1 mL) and ready dispensingof droplets. Droplet operations region 422 may have a gap height (H1)which is smaller (e.g., 250-500 μm) than H2 that facilitates, forexample, rapid transport, mixing, washing, and/or incubation of one ormore droplets. The reduction in gap height from H2 to H1 is such that acertain height ratio H2:H1 is maintained to provide for efficientdispensing of droplets. Gap height requirements for samplestorage/dispensing (H2) and other droplet operations (H1) on dropletactuator 400 may be described as H2≧H1.

Examples of different gap heights for a two-step droplet actuator areshown in Table 1. All gap heights shown in Table 1 (e.g., dropletactuators 1 through 5) provided for transport (e.g., electrowetting) ofdroplets from H2 to H1. However, as H2:H1 increases, dispensing offluids from H2 to H1 may be less efficient. For a given voltage, thefactors that affect the ability to dispense from H2 to H1 depend on theratio of H2:H1 and the interfacial tension of the droplet with the solidsubstrates.

TABLE 1 Variation of H 1 and H2 gap heights Droplet Actuator H1 H2Quantity 1 550-600 μm ~1.5 mm   2 2 550-600 μm ~3 mm 2 3 550-600 μm ~5mm 2 4 275-300 μm ~1 mm 2 5 275-300 μm ~2 mm 2

In another embodiment, variation in gap height from a sample storage anddispensing region to a droplet operations region may transition from H2to H1 to H0, e.g., a three-step transition. For example, H2 may be about5 mm, H1 may be about 1 mm, and H0 may be about 300-600 μm. In someembodiments, H2:H1 is about equal to H1:H0. H1 may, for example, rangefrom about 1 μm to about 2000 μm, or from about 10 μm to about 1000 μm,or from about 50 μm to about 750 μm. H2 may range from about 0.1 mm toabout 10 mm, or from about 1 mm to about 7.5 mm, or from about 15 mm toabout 5 mm.

FIGS. 5A, 5B, and 5C illustrate other top views of droplet actuator 400of FIGS. 4A and 4B and show a process of concentrating and dispensingmagnetically responsive beads from a large sample volume. The processshown in FIGS. 5A, 5B, and 5C is an example of a method wherein a largesample volume is manipulated as a single droplet in a process ofconcentrating and dispensing magnetically responsive beads.

Droplet actuator 400 may contain a quantity (e.g., about 1 mL) of samplefluid 510. In one embodiment, sample fluid may contain DNA to beevaluated by PCR analysis. Sample fluid 510 may contain a quantity ofmagnetically responsive beads 512, such as nucleic acid capture beads(e.g., ChargeSwitch beads). A magnet 514 is provided in proximity tocertain sample dispensing electrodes 424 within sample dispensing region420 for retaining a quantity of magnetically responsive beads. Inparticular, magnet 514 is arranged such that sample dispensing electrode424 a is within the magnetic field thereof. Magnet 514 may, for examplebe a permanent magnet or an electromagnet. Alternative magnetarrangements and positioning for attraction and collection ofmagnetically responsive beads are described in reference to FIG. 15 andFIG. 16.

An example of a process of concentrating and dispensing a quantity ofmagnetically responsive beads from a large sample volume on a dropletactuator may include, but is not limited to, the following steps.

In one step, FIG. 5A shows sample fluid 510, with magneticallyresponsive beads 512 therein, that is positioned at sample dispensingelectrodes 424 c and 424 d, which is within sample dispensing region 420(gap height H2) and away from magnet 514. Because sample fluid 510 ispositioned away from and out of the magnetic field of magnet 514,magnetically responsive beads 512 are dispersed somewhat evenlythroughout the volume of sample fluid 510. Sample dispensing electrodes424 c and 424 d are activated (turned ON).

In another step, FIG. 5B shows a finger of sample fluid 510 that isformed by extending the liquid atop adjacent sample dispensingelectrodes 424. In this step, sample dispensing electrodes 424 a and 424b, and optionally 424 c, are activated (turned ON). Finger of samplefluid 510 is drawn along sample dispensing electrodes 424 b and 424 a,which is away from sample dispensing electrodes 424 c and 424 d andtoward magnet 514. At sample dispensing electrode 424 b, the height ofgap 414 transitions from H2 to H1, e.g., the height of gap 414 getssmaller from H2 to H1. The magnetic force of magnet 514 concentratesmagnetically responsive beads 512 in a region of the finger that isclosest to magnet 514.

In another step, FIG. 5C shows a bead droplet 516 that is formed atopsample dispensing electrode 424 a. In this step, sample dispensingelectrodes 424 b and 424 c are deactivated (turned OFF) and sampledispensing electrode 424 e is activated (turned ON). Sample dispensingelectrodes 424 a and 424 d remain activated. As a result, the finger ofsample fluid 510 snaps off and bead droplet 516 is formed atop sampledispensing electrode 424 a within gap height H1.

The method of the invention may be used to create a high concentrationof magnetically responsive beads 512 in a single bead containing dropletfrom a relatively large sample volume (e.g., about 1 mL). Once thehighly concentrated magnetically responsive bead droplet 516 is formed,it may be subjected to other droplet operations within droplet actuator400.

In another embodiment, the process shown in FIG. 5 may be used to form asingle bead containing droplet in a droplet actuator where the gapheight transitions from H2 to H1 to H0 (H0≦H1≦H2).

FIGS. 6A and 6B illustrate a top view and a side view, respectively, ofa droplet actuator 600 and illustrate variations in gap heightassociated with sample storage and waste disposal regions. Dropletactuator 600 is an example of a droplet actuator that is configured forstorage of large volumes of sample fluid and waste fluid.

Droplet actuator 600 may include a bottom substrate 610 and a topsubstrate 612 that are separated by a gap 614. Bottom substrate 610 mayinclude an arrangement of droplet operations electrodes 618 (e.g.,electrowetting electrodes). Droplet operations are conducted atopdroplet operations electrodes 618 on a droplet operations surface.Droplet actuator 600 may include certain regions for storing samplefluids and waste fluids. For example, droplet actuator 600 may include,but is not limited to, a sample dispensing region 620 (e.g., storage anddispensing) and a waste disposal region 622 that are interconnected by adroplet operations region 624. The height of gap 614 at each region mayvary.

One or more sample dispensing electrodes 626, e.g., sample dispensingelectrodes 626 a through 626 e may be positioned within sampledispensing region 620 on bottom substrate 610. Sample dispensingelectrodes 626 may, for example, be used to manipulate a large volume ofsample fluid (e.g., about 1 mL) that contains a quantity of magneticallyresponsive beads for processing within droplet actuator 600. One or morewaste disposal electrodes 628, e.g., waste disposal electrodes 628 athrough 628 d, may be positioned within waste disposal region 622 onbottom substrate 610. Sample dispensing electrodes 626 and wastedisposal electrodes 628 are interconnected by a path or array of dropletoperations electrodes 618 within droplet operations region 624.

The configuration of electrodes in droplet actuator 600 is such that oneor more droplets (not shown) may be dispensed from sample dispensingelectrodes 626 onto droplet operations electrodes 618 for transport andprocessing within droplet actuator 600. The variability in gap heightthat may be associated with different processing regions, e.g., sampledispensing region 620, waste disposal region 622, and droplet operationsregion 624, in droplet actuator 600 is illustrated in FIG. 6B. In thisexample, two different gap heights along gap 614 may be associated withthe different processing regions. Sample dispensing region 620 and wastedisposal region 622 of droplet actuator 600 may have a certain gapheight (H2) that is sufficiently large to facilitate storage of largerliquid volumes and ready dispensing and disposal of droplets. Dropletoperations region 624 may have a gap height (H1) which is smaller thanH2 that facilitates, for example, rapid transport, mixing, washing,and/or incubation of one or more droplets. The reduction in gap heightfrom H2 to H1 is such that a certain height ratio H2:H1 is maintained toprovide for efficient dispensing of droplets. The increase in gap heightfrom H1 to H2 is such that waste fluid disposed within disposal region622 is effectively retained.

FIGS. 7 A and 7B illustrate another top view and side view,respectively, of droplet actuator 400 of FIGS. 4A and 4B and illustrateanother example of a two-step droplet actuator configured for integratedsample-to-result analysis of a single biological sample. Theconfiguration of droplet actuator 400 shown in FIGS. 7A and 7B issubstantially the same as shown in FIGS. 4A and 4B except that anoff-actuator sample reservoir is associated with droplet actuator 400.For example, a substrate 710 may be provided atop top substrate 414.Substrate 710 may include a sample reservoir 712 for containing aquantity of sample fluid. Substrate 710 may, for example, be formed ofplastic, glass or another suitable substrate. An opening 714 is providedwithin top substrate 412, establishing a fluid path from samplereservoir 712 into gap 414 into sufficient proximity with certaindroplet operations electrodes 418 to permit the electrode to interactwith a liquid flowed through the fluid path.

FIG. 8 illustrates yet another side view of a portion of dropletactuator 400 of FIGS. 4A and 4B and illustrates the interface betweendroplet operations and waste disposal regions where the gap heighttransitions from H1 to H2. In this example, two different gap heightsalong gap 414 may be associated with the different processing regions. Awaste disposal region 810 of droplet actuator 400 may have a certain gapheight (H2) that is sufficiently large to facilitate storage of largerliquid volumes (e.g., about 1 mL). A droplet operations region 812 mayhave a gap height (H1) which is smaller than H2 that facilitates, forexample, rapid transport of one or more droplets. Pressure differencesbetween H1 (higher pressure area) and H2 (lower pressure area)facilitate transport of waste droplets into waste disposal region 810.For example, one or more waste droplets (not shown) may be transportedusing droplet operations (e.g., electrowetting) along droplet operationselectrodes 418 in gap region H1 to waste disposal electrodes 428 at theinterface of gap H2. Because the surfaces of a droplet actuator aretypically hydrophobic and the differences in pressure from H1 to H2,waste droplets are effectively pulled into waste disposal region 810.The variability in gap height is such that a large volume waste fluiddisposed within disposal region 810 is effectively retained.

In another embodiment, the waste disposal region described in referenceto FIGS. 6A and 6B and FIG. 8 may be eliminated. In this example, thesample dispensing region may function as a waste disposal region afterthe sample has been dispensed. The transition in gap height from adroplet operations region (H1) to the sample dispensing region (H2) isof sufficient height to effectively retain a large volume of wastefluid.

FIGS. 9A and 9B illustrate yet another top view and side view,respectively, of droplet actuator 400 of FIGS. 4A and 4B and illustratean example of a three-step droplet actuator configured for integratedsample-to-result analysis of a single biological sample. In thisexample, top substrate 412 of FIG. 4 is replaced with a top substrate912, where the gap height of a sample storage and dispensing region isincreased such that the overall footprint of the droplet actuator isdecreased. An intermediate gap height region is provided such that largepressure differences associated with dispensing from a larger gap heightto a smaller gap height are significantly reduced. In this example,variations in gap height associated with certain droplet operationsregions transition from H2 to H1 to H0 (H2≧H1≧H0).

A substrate 920 may be provided atop top substrate 912. Substrate 920may include a well 922 for containing a quantity of sample fluid.Substrate 920 may, for example, be formed of plastic, glass or anothersuitable substrate. An opening 944 is provided within top substrate 912,establishing a fluid path from well 922 into gap 414 into sufficientproximity with certain droplet operations electrodes 918 to permit theelectrode to interact with a liquid flowed through the fluid path.

Droplet actuator 400 may include certain regions for performing certainprocess steps. For example, droplet actuator 400 may include, but is notlimited to, a sample dispensing region 926 (e.g., storage anddispensing), an intermediate dispensing region 928, and a dropletoperations region 930 (e.g., mixing, incubation, washing, detection).The height of gap 414 at each region may vary. Sample dispensing region926 of droplet actuator 900 may have a certain gap height (H2) that issufficiently large to facilitate storage of larger liquid volumes (e.g.,about 1 mL) in a smaller amount of x-y space. Intermediate sampledispensing region 928 may have a certain gap height (H1) which issmaller than H2 that facilitates dispensing of sample fluid from a largegap height to a smaller gap height. Droplet operations region 930 mayhave a gap height (H0) which is even smaller than H1 that facilitatesdroplet operations such as rapid transport, mixing, washing, and/orincubation of one or more droplets. The reduction in gap height from H2to H1 to H0 (H0≦H1≦H2) is such that a certain height ratio H2:H1 isapproximately equivalent to the ratio of H1:H0. Large pressuredifferences between H2 and H0 are minimized by the transition throughgap height H1.

FIG. 10 illustrates yet another top view of droplet actuator 400 ofFIGS. 4A and 4B and illustrates an example of suitable dimensions of thedroplet actuator. Each droplet operations electrode 418 may, for examplehave a dimension of about 2.125 mm×2.12 mm. Bottom substrate 410 mayinclude an arrangement of larger sample dispensing electrodes 424 (e.g.,sample dispensing electrodes 424 c, 424 d, and 424 e) and smaller sampledispensing electrodes 424 (e.g., sample dispensing electrodes 424 a and424 b). Each larger sample dispensing electrode may, for example, beabout 6.75 mm×13.5 mm in size. Each smaller sample dispensing electrodemay, for example, be about 6.75 mm×6.75 mm in size. Bottom substrate 410may include an arrangement of reagent dispensing electrodes 426 (e.g., 4reagent dispensing electrodes 426). Each reagent dispensing electrodemay, for example, be about 6.75×6.75 mm in size.

7.2 Mixing

FIGS. 11 lA through 11C illustrate top views of an electrode arrangement1100 and show a process for mixing a small volume of fluid with a largervolume of fluid. The process shown in FIGS. 11A through 11C is anexample of a mixing process in which a small volume of fluid such as areagent fluid (e.g., magnetically responsive beads suspended in an assaybuffer) is combined using the process of diffusion with a larger volumeof fluid such as a sample fluid (e.g., about 1 mL of a biologicalsample).

Electrode arrangement 1100 may include a large sample dispensingelectrode 1110. Sample dispensing electrode 1110 may, for example, bepositioned within a sample dispensing region with a gap height of H2 asdescribed in reference to FIGS. 7A and 7B. One or more smaller, narrowmixing electrodes 1112 may be positioned within sample dispensingelectrode 1110. In this example, three narrow mixing electrodes 1112 arearranged in parallel within sample reservoir electrode 1110; however,any number or arrangement (e.g., arranged in a grid pattern) of narrowmixing electrodes 1112 may be used. The number and spacing betweensuccessive narrow mixing electrodes 1112 may, for example, be determinedby the diffusion rate of the two fluids to be mixed. The arrangement ofnarrow mixing electrodes 1112 within sample dispensing electrode 1110 issuch that a sufficiently large interface area for diffusion is createdbetween a reagent fluid in narrow mixing electrodes 1112 and a samplefluid in sample dispensing electrode 1110.

An example of a mixing method that uses diffusion to mix a smallervolume of reagent fluid with a larger volume of sample fluid mayinclude, but is not limited to, the following steps.

In one step, FIG. 11B shows a volume of reagent fluid 1114 loaded (e.g.,by electrowetting) in narrow mixing electrodes 1112. Reagent fluid 1114may, for example, be about 10 or about 15 or about 25 μL in volume.Reagent fluid 1114 may, for example, include a quantity of magneticallyresponsive beads for distribution in a sample fluid. In another example,reagent fluid 1114 may be another reagent fluid without a quantity ofmagnetically responsive beads.

In another step, FIG. 11C shows a larger volume of sample fluid 1116loaded on sample dispensing electrode 1110. As sample fluid 1116 isloaded on sample dispensing electrode 1110, mixing of sample fluid 1116and reagent fluid 1114 occurs by diffusion.

FIGS. 12A and 12B illustrate top views of an electrode arrangement 1200and show another process for mixing a larger volume of fluid. Theprocess shown in FIGS. 12A and 12B is an example of a mixing process inwhich the inherent circulation at one or more electrode edges is used topromote mixing of a larger volume of fluid (e.g., about 1 mL).

Electrode arrangement 1200 may include a large dispensing electrode1210. Dispensing electrode 1210 may, for example, be positioned within asample dispensing region with a gap height of H2 as described inreference to FIGS. 7A and 7B. One or more smaller, mixing electrodes1212 may be situated within dispensing electrode 1210. In one example,four round mixing electrodes 1212 a through 1212 d are arranged withindispensing electrode 1210. The number and spacing between round mixingelectrodes 1212 may, for example, be determined by interfacial tensionof the fluids to be mixed.

An example of a mixing process in which the inherent circulation at oneor more electrode edges is used to promote mixing of a larger volume offluid may include, but is not limited to, the following steps.

In one step, FIG. 12A shows a volume of fluid 1214 loaded on dispensingelectrode 1210 and mixing electrodes 1212. Fluid 1214 may, for example,be a volume of sample fluid that contains a quantity of reagent fluid,e.g., magnetically responsive beads, for dispersion within the samplefluid. Dispensing electrode 1210 and mixing electrodes 1212 areactivated (turned ON).

In another step, FIG. 12B shows certain mixing electrodes 1212, e.g.,mixing electrodes 1212 a and 1212 d, turned OFF (deactivated). As mixingelectrodes 1212 a and 1212 d are turned OFF, fluid 1214 is cleared frommixing electrodes 1212 a and 1212 d. Circulation of fluid 1214 occurs atthe edges of the OFF electrodes. By activating and deactivating mixingelectrodes 1212 in, for example, a random pattern, mixing occurs acrossthe volume of fluid 1214.

FIG. 13 illustrates a side view of an example of an on-actuator samplereservoir 1300 of a droplet actuator and illustrates a method of mixinglarge volumes of liquid with smaller volumes of reagents. The processshown in FIG. 13 is an example of a mixing method that uses manualpipetting of a sample fluid into and out of an on-actuator samplereservoir to mix larger volumes of sample fluid with a smaller volume ofreagent fluid.

Sample reservoir 1300 may include a bottom substrate 1310 and a topsubstrate 1312 that are separated by a gap 1314. A gasket 1316 may beused to provide a seal around the sample reservoir 1300. Bottomsubstrate 1310 may include an arrangement of sample dispensingelectrodes 1318 (e.g., electrowetting electrodes). An opening 1320 isprovided within top substrate 1312. Opening 1320 establishes a fluidpath into gap 1314 and onto sample dispensing electrodes 1318 on bottomsubstrate 1310. Opening 1320 may be of sufficient size to accommodatethe tip of a fluid delivery device 1322. In one example, fluid deliverydevice 1322 may be a pipette that includes a pipette tip 1324. In thisexample, opening 1320 is of sufficient size to accommodate pipette tip1324.

In operation, a small volume of reagent fluid (e.g., about 3-6 μL) ispreloaded in sample reservoir 1300. In one example, the reagent fluidmay include a quantity of beads 1326. Fluid delivery device 1322 is usedto introduce a larger volume of fluid 1328 (e.g., sample fluid of about1 mL) into sample reservoir 1300 through opening 1320. Fluid 1328 isrepeatedly pipetted into and out of sample reservoir 1300 throughopening 1320 and pipette tip 1324 using fluid delivery device 1322. Asfluid 1328 is repeatedly pipetted into and out of sample reservoir 1300and pipette tip 1324, beads 1326 are substantially dispersed withinfluid 1328.

FIG. 14 illustrates a side view of an example of a portion of a dropletactuator 1400 and illustrates another method of mixing a larger volumeof fluid with a smaller volume of fluid. The process shown in FIG. 14 isan example of a mixing method that uses one or more off-actuatorreservoirs and electrowetting to mix a larger volume of sample fluidwith a smaller volume of reagent fluid in an on-actuator samplereservoir.

Sample reservoir 1400 may include a bottom substrate 1410 and a topsubstrate 1412 that are separated by a gap. A gasket 1416 may be used toprovide a seal around the sample reservoir 1400. A certain area betweenbottom substrate 1410 and top substrate 1412 forms an on-actuator samplereservoir 1414. Bottom substrate 1410 may include an arrangement ofsample dispensing electrodes 1418 within on-actuator sample reservoir1414, e.g., sample dispensing electrodes 1418 a through 1418 c (e.g.,electrowetting electrodes). Top substrate 1412 may, for example, beformed of a molded material such that one or more off-actuatorreservoirs 1420, e.g., reservoirs 1420 a, 1420 b, and 1420 c, areformed. Gating electrodes (not shown) may be positioned in proximity ofeach off-actuator reservoir 1420. The gating electrodes are used tocontrol the flow of fluid into and out of one or more selectedoff-actuator reservoir 1420. Off-actuator reservoirs 1420 may be ofsufficient size to contain a large volume of fluid, e.g., about 1 mL.Corresponding to off-actuator reservoirs 1420 a, 1420 b, and 1420 c areopenings 1422 a, 1422 b, and 1422 c, respectively. Openings 1422 a, 1422b, and 1422 c establish a fluid path from off-actuator reservoirs 1420a, 1420 b, and 1420 c into on-actuator sample reservoir 1414.

In operation, a volume of fluid 1424 (e.g., about 1 mL) is drawn fromone or more off-actuator reservoirs 1420 through the fluid path intoon-actuator sample reservoir 1414 of droplet actuator 1400. Fluid 1424may, for example, be a sample fluid that includes a quantity ofmagnetically responsive beads 1426. In one embodiment, a singleoff-actuator reservoir 1420, e.g., off-actuator reservoir 1420 a, isused to load fluid 1424 into on-actuator sample reservoir 1414. In thisexample, reservoir electrode 1418 a is activated and fluid 1424 is drawnfrom off-actuator reservoir 1420 a through opening 1422 a of topsubstrate 1412 and onto reservoir electrode 1418 a. To mix fluid 1424and beads 1426 therein, the entire volume (or the majority of thevolume) of fluid 1424 is repeatedly transferred from on-actuator samplereservoir 1414 through opening 1422 a into off-actuator reservoirs 1420a. In this step, reservoir electrode 1418 a is deactivated (turned OFF)and fluid 1424 is drawn back into off-actuator reservoir 1420 a bycapillary forces. As fluid 1424 is repeatedly transferred into and outof on-actuator sample reservoir 1414, beads 1426 are substantiallydispersed within fluid 1424.

In another embodiment, fluid 1424 is repeatedly transferred into and outof on-actuator sample reservoir 1414 using two or more off-actuatorreservoirs 1420, e.g., three reservoirs 1420, e.g., reservoirs 1420 a,1420 b, and 1420 c. By randomly selecting one or more off-actuatorreservoirs 1420 (e.g., activation/deactivation of gating electrodes),more effective mixing is achieved.

In yet another embodiment, an electrode may be provided in eachoff-actuator reservoir 1420 to facilitate the flow of fluid 1424 fromon-actuator sample reservoir 1414 into the off-actuator reservoirs 1420.

FIG. 15 illustrates a side view of a portion of a droplet actuator 1500and illustrates another method of mixing a large volume of fluid in adroplet actuator. The process shown in FIG. 15 is an example of a mixingmethod that uses static electrowetting to mix a large volume of fluid inan on-actuator sample reservoir.

Droplet actuator 1500 may include a bottom substrate 1510 and a topsubstrate 1512 that are separated by a gap 1514. Droplet actuator 1500may include a sample dispensing region 1516 (e.g., storage anddispensing) and a droplet operations region 1518 (e.g., transporting,incubation, washing). The height of gap 1514 at each region may vary.Sample dispensing region 1516 of droplet actuator 1500 may have acertain gap height (H2) that is sufficiently large to facilitate storageof large volume of fluid (e.g., about 1 mL). Droplet operations region1518 may have a gap height (H1), which is smaller than H2, thatfacilitates droplet operations such as rapid transport, mixing, washing,and/or incubation of one or more droplets.

One or more sample dispensing electrodes 1520, e.g., two sampledispensing electrodes 1520 a and 1520 b, may be provided within sampledispensing region 1516 on bottom substrate 1510. In a preferredembodiment, a coplanar reference electrode 1522 may be positionedbetween sample dispensing electrodes 1520. In this example, becausereference electrode 1522 is arranged with sample dispensing electrodes1520, a conductive coating typically applied to the top substrate of adroplet actuator is not required.

An example of a mixing method that uses static electrowetting to mix alarge volume of fluid in an on-actuator sample reservoir may include,but is not limited, to the following steps.

In one step, FIG. 15A shows a volume of fluid 1524 loaded in sampledispensing region 1516 on sample dispensing electrodes 1520. Fluid 1524may, for example, be a volume of sample fluid that contains a quantityof reagent fluid, e.g., magnetically responsive beads, for dispersionwithin the sample fluid. Sample dispensing electrodes 1520 are turnedOFF (inactive). Because sample dispensing electrodes 1520 are inactive,sample fluid 1524 has a rounded shape and is sandwiched between topsubstrate 1512 and bottom substrate 1510.

In another step, FIG. 15B shows sample dispensing electrodes 1520 turnedON (activated). As sample dispensing electrodes 1520 are activated,sample fluid 1524 is spread out over sample dispensing electrodes 1520into a flattened shape and mixing occurs within sample fluid 1524. Byrepeatedly activating and deactivating sample dispensing electrodes1520, e.g., pulsing the sample fluid, efficient mixing of sample fluid1524 occurs.

In various other embodiments, the arrangement of sample dispensingelectrodes and interspersed coplanar reference electrodes may be usedwithin the larger gap height regions (H2) of a droplet actuator thatincludes variations in gap heights. Because a coplanar referenceelectrode arrangement is used, the conductive coating typically appliedto the top substrate of a droplet actuator is not required.

In another embodiment, a piezoelectric strip (not shown) may be used toprovide a sufficient amount of voltage to agitate and mix a samplefluid. In this example, the piezoelectric strip may be positioned atopthe top substrate of the droplet actuator or below the droplet actuatoror within the droplet actuator.

7.3 Bead Collection

FIGS. 16A and 16B illustrate yet other top views of droplet actuator 400of FIGS. 4A and 4B and illustrate the arrangement of one or more magnetsthat may be used to concentrate and collect a quantity of magneticallyresponsive beads from a large sample volume. In one embodiment,referring to FIG. 16A, a magnet 1610 may be positioned in proximity tosample dispensing electrode 424 a within droplet operations region 422(gap height H1). In particular, magnet 1610 is arranged such that sampledispensing electrodes 424 a through 424 e are within the magnetic fieldthereof. Magnet 1610 may, for example, be a permanent magnet or anelectromagnet. The magnetic force of magnet 1610 may be used toconcentrate a quantity of magnetically responsive beads (not shown) in aregion of sample fluid (not shown) that is closest to magnet 1610. Anexample of a magnet-based bead concentration and collection protocol isdescribed in reference to FIGS. 5A, 5B, and 5C.

In another embodiment and referring to FIG. 16B, a series of magnets1610 with increasing magnetic field strength may be positioned inproximity to certain sample dispensing electrodes 424. It should benoted that the magnets may be of the same strength but may be positionedat differing distances from the droplet operation gap such that agradient of increasing magnetic field strength is established in thegap. In one example, four magnets 1610 of different magnetic fieldstrengths may be used to achieve a progressively increasing magneticfield strength across sample dispensing electrodes 424. For example, amagnet 1610 d with a low magnetic field strength (S1) may be positionedin proximity of sample dispensing electrodes 424 d and 424 e. A magnet1610 c with a greater magnetic field strength (S2) may be positioned inproximity of sample dispensing electrode 424 d. A magnet 1610 b with ayet greater magnetic field strength (S3) may be positioned in proximityof sample dispensing electrodes 424 c and 424 b. A magnet 1610 a with astill greater magnetic field strength (S4) may be positioned inproximity of sample dispensing electrode 424 a. In this example, theincrease in the magnetic field strength of magnets 1610 may be describedas a gradient wherein S1≧S2≧S3≧S4. The magnetic field gradient is suchthat magnetically responsive beads are pulled from sample dispensingelectrode 424 e towards sample dispensing electrode 424 a.

In yet another embodiment, a magnet 1610 may be a movable magnet (notshown). In this example, magnet 1610 may be positioned over or underdroplet actuator 400 such that magnet 1610 is aligned with and movablealong the path of sample dispensing electrodes 424. In one example, avolume of sample fluid, with magnetically responsive beads therein, maybe positioned at sample dispensing electrodes 424 c and 424 e andaligned with magnet 1610. Because of the magnetic force of magnet 1610,the magnetically responsive beads are held at the surface of sampledispensing electrodes 424 c and 424 d. As magnet 1610 is moved towardsample dispensing electrode 424 a, the magnetically responsive beads arepulled toward sample dispensing electrode 424 a.

FIG. 17 illustrates a side view of a portion of a droplet actuator 1700that includes a strong magnet positioned a certain distance away fromthe bottom surface of the droplet actuator. Typically, a magnet ispositioned in close proximity to the bottom substrate of a dropletactuator for attracting a quantity of magnetically responsive beads in asample. Consequently, for a large sample volume, magnetically responsivebeads that are closest to the magnet are strongly attracted to magnet,while beads within the sample that are further away from the magnetexhibit substantially little or no attraction to the magnet. Dropletactuator 1700 of the invention is positioned near a magnet that providesa magnetic field strength that is suitably large such that substantiallyall magnetically responsive beads in a large sample volume are withinthe magnetic field of the magnet, albeit the beads may be experiencingdifferent magnetic field strengths because of some amount of magneticfield gradient.

Droplet actuator 1700 may include a bottom substrate 1710 and a topsubstrate 1712 that are separated by a gap 1714. Droplet actuator 1700may include a sample dispensing region 1716 (e.g., storage anddispensing) and a droplet operations region 1718 (e.g., transporting,incubation, washing). In one example, sample dispensing region may spanabout 3 cm in length. The height of gap 1714 at each region may vary.Sample dispensing region 1716 of droplet actuator 1700 may have acertain gap height (H2) that is sufficiently large to facilitate storageof large volume of fluid. Droplet operations region 1718 may have a gapheight (H1) which is smaller than H2 that facilitates droplet operationssuch as rapid transport, mixing, washing, and/or incubation of one ormore droplets. One or more sample dispensing electrodes 1720 may beprovided within sample dispensing region 1716 on bottom substrate 1710.A volume of sample fluid 1722 may be positioned atop sample dispensingelectrodes 1720 within sample dispensing region 1716. Sample fluid 1722may span the length of sample dispensing region 1716, e.g., about 3 cm.Sample fluid 1722 may, for example, be about a 1 mL sample droplet thatincludes a quantity of magnetically responsive beads 1724.

A magnet 1726 may be positioned at a certain distance away from andbelow bottom substrate 1710. Magnet 1726 may, for example, be a strongpermanent magnet or a strong electromagnet. The distance between magnet1726 and sample dispensing electrodes 1720 provides a gradient ofmagnetic field strength from magnet 1726 across sample dispensing region1716. Further, magnet 1726 is suitably strong such that substantiallyall of the volume of sample fluid 1722 is within the magnetic field ofmagnet 1726. That is, substantially all magnetically responsive beads1724 in sample fluid 1722 are within the magnetic field of the magnet,albeit the magnetically responsive beads 1724 may be experiencingdifferent magnetic field strengths because of some amount of magneticfield gradient. Magnet 1726 may be positioned such that its magneticfield strength is greater at H1 than at H2. Consequently, a magneticfield gradient is formed such that magnetically responsive beads areattracted from H2 toward H1, which is toward the stronger magnetic fieldstrength of magnet 1726).

7.4 Droplet Transport

FIGS. 18A through 18C illustrate top views of an electrode arrangement1800 of a portion of a droplet actuator and illustrate a process oftransporting a small droplet onto a reservoir electrode. The processshown in FIGS. 18A through 18C is an example of a transporting methodthat uses droplet “stretching” to prevent fracturing of the droplet intoseveral smaller droplets when entering a reservoir. Fracturing of adroplet during transport into a reservoir may interfere with subsequentprocessing steps such as mixing and dispensing.

Electrode arrangement 1800 may include a reservoir electrode 1810. Anarrangement of droplet operations electrodes 1812 feeds into reservoirelectrode 1810. A droplet 1814 may be positioned on a certain dropletoperations electrode 1812 for transporting onto reservoir electrode1810.

An example of a transport process in which a droplet is “stretched” toprevent fracturing of the droplet into several smaller droplets whenentering a reservoir may include, but is not limited to, the followingsteps.

In one step, FIG. 18A shows droplet 1814 positioned on a certain dropletoperations electrode 1812 several electrodes (e.g., 3 droplet operationselectrodes 1812 a, 1812 b, and 1812 c) away from reservoir electrode1810.

In another step, FIG. 18B shows droplet 1814 stretched across 3 dropletoperations electrodes 1812. Droplet 1814 is slowly stretched acrossadjacent droplet operations electrodes 1812 by sequentially activating(turning ON) adjacent electrodes. Droplet operations electrodes 1812 maybe activated in a sequential manner or in a substantially simultaneousmanner, causing droplet 1814 to stretch and extend along all threeelectrodes.

In another step, FIG. 18C shows droplet 1814 positioned on reservoirelectrode 1810. Once droplet 1814 is stretched, droplet operationselectrodes 1812 are deactivated (turned OFF) and reservoir electrode1810 is activated (turning ON), causing droplet 1814 to move intoreservoir electrode 1810. Droplet operations electrodes 1812 may beturned OFF in a sequential manner or in a substantially simultaneousmanner.

7.5 Sample Containment

Variation in gap height from a sample dispensing region to a dropletoperations region may, for example, transition from a large gap height(H2) to a smaller gap height (H1). In one example, a sample dispensingregion may have a gap height (H2) of about 5 mm and a droplet operationsregion may have a gap height (H1) of about 550-600 μm. At larger gapheights of about 5 mm, the height of a sample fluid (e.g., about 1 mL)within the sample dispensing region may be less than the available gapheight, e.g., the sample fluid does not exit to the top substrate due tothe effect of gravity. Because the sample fluid is not in contact withthe top substrate, the sample fluid may flow uncontrolled out of the H2gap and into the H1 gap (droplet operations region) when the sampledispensing electrodes are activated (turned ON).

FIGS. 19A through 19D illustrate side views of a portion of a dropletactuator 1900 and illustrate methods for containing the sample space ofan on-actuator reservoir. The processes shown in FIGS. 19A through 19Dare examples of fluid containment methods that prevent uncontrolled flowof a sample fluid from a large gap height (H2) into a smaller gap height(H1) when sample dispensing electrodes within the on-actuator reservoirare activated. In one embodiment, the droplet actuator may includehydrophilic patches for sample fluid retention. In another embodiment,the droplet actuator may include physical structures for sample fluidretention. In yet another embodiment, the ratio of H2:H1 may beincreased such that a greater pressure difference between H1 (higherpressure area) and H2 (lower pressure area) is formed.

Droplet actuator 1900 may include a bottom substrate 1910 and a topsubstrate 1912 that are separated by a gap 1914. Droplet actuator 1900may include a sample dispensing region 1916 (e.g., storage anddispensing) and a droplet operations region 1918 (e.g., transporting,incubation, washing). The height of gap 1914 at each region may vary.Sample dispensing region 1916 of droplet actuator 1900 may have acertain gap height (H2) that is sufficiently large to facilitate storageof large volume of fluid (e.g., about 1 mL). Droplet operations region1918 may have a gap height (H1) which is smaller than H2 thatfacilitates droplet operations such as rapid transport, mixing, washing,and/or incubation of one or more droplets. One or more sample dispensingelectrodes 1920 may be provided within sample dispensing region 1916 onbottom substrate 1910. A sample fluid droplet 1922 may be positionedatop sample dispensing electrode 1920 within sample dispensing region1916. Sample fluid droplet 1922 may, for example, be about a 1 mL,sample droplet.

FIG. 19A illustrates a preferred state of sample fluid droplet 1922within sample dispensing region 1916. In this example, when sampledispensing electrode 1920 is activated (turned ON), sample fluid droplet1922 is in a rounded shape and extends to and contacts top substrate1912 within sample dispensing region 1916. Sample fluid droplet 1922 iscontained within sample dispensing region 1916.

Referring to FIG. 19B, at larger gap heights, e.g., about 5 mm, theheight of sample fluid droplet 1922 within the sample dispensing region1916 is less than the available gap height, e.g., the sample fluid doesnot extent to top substrate 1912 due to the effect of gravity. Becausethe sample fluid droplet 1922 is not in contact with top substrate 1912,the sample fluid may flow uncontrolled out of the H2 gap and into the H1gap (e.g., droplet operations region 1918) when sample dispensingelectrode 1920 is activated (turned ON).

Sample fluid droplet 1924 may be contained within sample dispensingregion 1916 by incorporation of chemical and/or physical structureswithin sample dispensing region 1916. In one embodiment, dropletactuator 1900 may include hydrophilic patches for assisting in samplefluid retention. Referring to FIG. 19C, one or more hydrophilic patches1924 may be disposed within sample dispensing region 1916 on the surfaceof top substrate 1912 that is facing gap 1914. Similarly, one or morehydrophilic patches may be disposed on bottom substrate 1910 that isfacing gap 1914. Hydrophilic patches 1924 have affinity to aqueoussample fluid droplet 1924 such that sample fluid droplet 1924 isretained in sample dispensing region 1916 when sample dispensingelectrode 1920 is activated (turned ON).

In another embodiment, droplet actuator 1900 may include physicalstructures for sample fluid retention. Referring to FIG. 19D, a physicalstructure 1926 may be provided on, for example, the surface of topsubstrate 1912 that is facing gap 1914. Physical structure 1926 may, forexample, be a ring structure that extends from top substrate 1912 to thetop surface of sample droplet 1924. Physical structure 1926 is designedto permit sample dispensing, while at the same time hinder uncontrolledflow of sample fluid 1924 from sample dispensing region 1916 (H2) intodroplet operations region 1918 (H1). In another example, physicalstructure 1926 may be provided on the surface of bottom substrate 1910that is facing gap 1914.

In yet another embodiment, the ratio of H2:H1 may be increased such thata greater pressure difference is between H1 (higher pressure area) andH2 (lower pressure area) is formed. The increase in pressure differencebetween H1 and H2 provides resistance to fluids flowing from H2 into H1and facilitates retention of sample fluid 1924 in sample dispensingregion 1916 (H2).

7.6 Detection System

The detection system of the invention uses a single excitation beam anda single detection beam to collect multiple (e.g. four) differentfluorescent signals at a single detection spot on a droplet actuator. Byusing an arrangement of light-emitting diodes (LEDs) that includesexcitation lenses, filters, and mirrors, multiple (e.g. four) differentexcitation wavelengths are multiplexed in a single excitation beam.Similarly, by using an arrangement of detectors (e.g. photo diodes) thatincludes mirrors, filters and detection lenses, a single optical beam isused for detection of the corresponding emission signals.

FIGS. 20A and 20B illustrate perspective views of two exampleembodiments of a detection system 2000 for detection of multiple (e.g.four) different fluorophores at a single detection spot. In one example,FIG. 20A shows an embodiment of detection system 2000 in which four LEDsand four detectors are arranged in a parallel configuration near thedroplet actuator. In another example, FIG. 20B shows an embodiment ofdetection system 2000 in which the four LEDs and four detectors arearranged in a “V” configuration near the droplet actuator.

Detection system 2000 may include multiple excitation LEDs 2010 that arealigned with multiple excitation lenses 2012, multiple excitationfilters 2014, and multiple mirrors 2016, respectively. By way ofexample, detection system 2000 may include four LEDs 2010 a through 2010d that are aligned with four excitation lenses 2012 a through 2012 d,four excitation filters 2014 a through 2014 d, and four mirrors 2016 athrough 2016 d, respectively. Each excitation lens 2012 is used to focuslight emitted from its corresponding LED 2010 onto the correspondingexcitation filter 2014. Each excitation filter 2014 is used to select acertain wavelength of light emitted from its corresponding LED 2010 thatmay be used for excitation of a certain fluorophore. Each mirror 2016 isused to direct the filtered light (e.g., light of a certain wavelength)to a corresponding second directing mirror 2018 that is positioned inproximity of a corresponding excitation focusing lens 2020. Eachdirecting mirror 2018 and corresponding focusing lens 2020 is used tomultiplex the different wavelengths of light (e.g., four differentwavelengths of light) into a single excitation beam.

Detection system 2000 may also include multiple detectors 2022 that arealigned with multiple detection lenses 2024, multiple detection filters2026, and multiple selective dichroic filters 2028, respectively. By wayof example, detection system 2000 may include four detectors 2022 athrough 2022 d that are aligned with four detection lenses 2024 athrough 2024 d, four detection filters 2026 a through 2026 d, and fourdichroic filters 2028 a through 2028 d, respectively. Each dichroicfilter 2028 is used to select a certain wavelength of lightcorresponding to the emission wavelength of a certain fluorophore. Afocusing lens 2030 and a directing mirror 2032 are used to multiplexdifferent wavelengths of light emitted from one or more fluorophores(e.g., four different fluorophores) into a single detection beam.

In operation, detection system 2000 (in either the parallelconfiguration of FIG. 20A or the “V” configuration of FIG. 20B) ispositioned in an instrument (not shown) that is a holding a dropletactuator, such as a droplet actuator 2034. Detection system 2000 ispositioned such that a single excitation beam of light and a singledetection beam are directed to a detection spot (not shown) on dropletactuator 2034.

In one embodiment and referring to FIG. 20A, the parallel configurationof LEDs and detectors of detection system 2000 is offset from dropletactuator 2034. In this example, the excitation (incident) beam and thedetection (emission) beam arc aligned in parallel. In thisconfiguration, the fluorimeter may, for example, be positioned off theback of the droplet actuator.

In another embodiment and referring to FIG. 20B, the “V” configurationof LEDs and detectors of detection system 2000 is positioned abovedroplet actuator 2034. In this configuration, the fluorimeter may, forexample, be positioned above droplet actuator 2034.

7.7 Thermal Control

The invention provides methods for controlling heat flow and minimizingthermal losses in one or more temperature control zones on a dropletactuator. In particular, the methods of the invention use alternativeconfigurations of the bottom substrate materials, e.g., printed circuitboard (PCB), to control the flow of heat around the PCB. Because theflow of heat around the PCB is controlled, different temperature controlzones may be defined and used to support multiple droplets undergoingdifferent reactions at the same time. Careful configuration of substratematerials allows minimal use of input heat to maintain temperaturezones, and droplets in those zones, at desired temperatures.

FIG. 21 illustrates a top view of an example of a portion of a dropletactuator 2100 and illustrates methods for controlling the flow of heatin certain regions (temperature control zones) of a droplet actuator.Droplet actuator 2100 may include a bottom substrate 2110. Bottomsubstrate 2110 may, for example, be a PCB or other polymeric substratethat includes a dielectric layer 2112. For a PCB substrate, dielectriclayer 2112 may, for example, be an FR4 layer. Bottom substrate 2110 mayinclude an arrangement of droplet operations electrodes 2114 (e.g.,electrowetting electrodes). Droplet operations are conducted atopdroplet operations electrodes 2114 on a droplet operations surface.Droplet actuator 2100 may include one or more temperature control zones2116, e.g., temperature control zones 2116 a and 2116 b, for performingcertain process steps. One or more heater elements 2118, e.g., twoheater elements 2118 a and 2118 b, may be provided in proximity tobottom substrate 2110 and aligned with certain droplet operationselectrodes 2114. Heater elements 2118 may be used to heat thetemperature of filler fluid that is in the gap (not shown) of dropletactuator 2100 and that is flowing through temperature control zones2116.

In one embodiment, the geometry of conductive materials, such as copper,on bottom substrate 2110 (e.g. the PCB) may be used to control the flowof heat in temperature control zones 2116, e.g., to maintain temperatureuniformity or to increase time to desired temperature in bottomsubstrate 2110 at temperature control zones 2116. In one example, acopper heat spreader 2120 (copper heat spreading pad) may be provided onthe same PCB layer as droplet operations electrodes 2114. In thisexample, heat spreader 2120 may be positioned adjacent to certaindroplet operations electrodes 2114. In another example, a copper heatspreader 2122 may be provided on a different PCB layer as dropletoperations electrodes 2114 (e.g., backside layer or layer adjacent toelectrode layer). Heat spreaders 2120 and 2122 may be used to maintaindifferent isothermal regions on droplet actuator 2100 such that thetemperature gradient (ΔT) across that region of the PCB is small.Because copper heat spreaders are used, smaller heater elements 2118 maybe used and thereby minimize the amount of input heat required tomaintain a droplet at a certain reaction temperature.

In another example, the amount of copper on bottom substrate 2110 thatsurrounds temperature control zones 2116 may be minimized (not shown) toreduce conductive loss of heat from the thermal control zone. Becauseexcess copper (or other conductive material) is reduced and conductiveheat loss is minimized, additional power input is not required tocompensate for potential heat loss.

In yet another example, the area covered by bottom-side traces (notshown) on bottom substrate 2110 and within temperature control zones2116 may be maximized. For example the area of the trace used to conductan electrowetting voltage to certain droplet operations electrodes 2114within temperature control zone 2116 may be increased. Because the areaof the trace is increased, more heat may be absorbed from heater element2118.

In yet another example, certain droplet operations electrodes 2114 thatare heated to the same temperature may be co-localized in the sametemperature control zone 2116. The distance between co-localized dropletoperations electrodes 2114 may be minimized such that thermal loss issubstantially reduced and heating accuracy is maintained. Dropletoperations electrodes 2114 may be tied using metal filled or plated viasto the same bottom-side copper heat spreading pad. The copper heatspreading pad may, for example, be sized to cover about the same area asthe co-localized droplet operations electrodes. Alternatively, equalarea may be provided for all bottom-side traces for each dropletoperations electrode in the same temperature control zone, with tracesgenerally sized to substantially cover the area of the copper heatspreading pad. Alternatively, equal area may be provided for allbottom-side traces for each droplet operations electrode in the sametemperature control zone, with traces generally sized to serve thefunction of a heat spreading pad.

In yet another example, the amount of copper in vias that are used tocouple droplet operations electrodes 2114 within temperature control2116 to bottom-side heat spreading pads (e.g., heat spreader 2122) maybe maximized. For example, the amount of copper used may be maximized byusing the larger sized vias and/or by increasing the number of viasused. Via plating thickness may also be specified to maximize the amountof copper connecting droplet operations electrodes 2114 to bottom-sideheat spreading pads.

another embodiment, the geometry of the dielectric material (e.g., FR4)on bottom substrate 2110 may be used to control (reduce) the flow ofheat around temperature control zones 2116. In one example, thethickness of dielectric layer 2112 may be minimized, e.g., from lessthan about 31 mils to about 1 mil. Mechanical means may be used toprovide physical support to areas on the PCB with substantially reduceddielectric material. Because heat is applied through dielectric layer2112, minimizing the thickness of dielectric layer 2112 minimizes thethermal resistance between heater 2118 and temperature control zone2116, minimizes the heat capacity of the PCB, and maximizes the in-planethermal resistance to other parts of the PCB. Reduction in the thicknessof dielectric layer 2112 maximizes the impact of heat spreaders 2120 and2122 which have the dominant thermal conductivity.

In another example, one or more cutouts in dielectric layer 2112, e.g.,cutouts 2124 a through 2124 c, may be used to further reduce thermalconduction around temperature control zone 2116. Materials with lowthermal conductivity (e.g., air, plastic) may be used to fill orreinforce cutouts 2124.

FIGS. 22A, 22B, and 22C illustrate top views of an example of a portionof a droplet actuator 2200 and illustrate methods for co-locatingtemperature control zones and associated heat spreaders on a dropletactuator. Droplet actuator 2200 may include a bottom substrate 2210.Bottom substrate 2210 may, for example, be a PCB. Bottom substrate 2210may include an arrangement of droplet operations electrodes 2212 (e.g.,electrowetting electrodes). Droplet operations are conducted atopdroplet operations electrodes 2212 on a droplet operations surface.Droplet actuator 2200 may include one or more temperature control zones2214, e.g., temperature control zones 2214 a through 2214 e, to be usedduring certain process steps. Bottom substrate 2210 may include one ormore heat spreaders (copper heat spreading pads) 2216, e.g., five heatspreaders 2216 a through 2216 e, for controlling the flow of heat withinassociated temperature control zones 2214. In one example, heatspreaders 2216 may be provided on a different PCB layer as dropletoperations electrodes 2212 (e.g., backside layer or layer adjacent toelectrode layer). Heat spreaders 2216 may be used to heat temperaturecontrol zones 2214 to the same temperature or to different temperatures.Temperature control zones 2214 that are heated to the same temperaturemay be thermally coupled. In one example, three different temperaturecontrol zones, such as three temperature control zones used for PCRassays, may be used. In this example, heat spreader 2216 a may be usedto heat a temperature control zone 2214 a to a temperature T1 that issuitable for performing certain process steps. Heat spreaders 2216 b and2216 d may be used to heat temperature control zones 2214 b and 2214 dto a second temperature T2 that is suitable for performing other processsteps. Heat spreaders 2216 c and 2216 e may be used to heat temperaturecontrol zones 2214 c and 2214 e to a third temperature T3 that issuitable for performing yet other process steps. One or more reactiondroplets (not shown) may be transported on droplet operations electrodes2212 using droplet operations into and out of temperature control zones2214 (e.g., cycling between temperatures T1, T2, and T3).

FIG. 22B shows one example of implementing the co-located temperaturecontrol zones and associated heat spreaders that are described in FIG.22A. In this example, one or more heater elements 2218 may be used toprovide heat to heat spreaders 2216. For example, five heater elements2218 a through 2218 e may be patterned directly underneath heatspreaders 2216 on bottom substrate 2210. Heater elements 2218 a through2218 e may, for example, be resistive heaters. Bottom substrate 2210 mayalso include one or more thermometers 2220, e.g., thermometers 2220 athrough 2220 e. Thermometers 2220 may, for example, be used astemperature sensors used to monitor and regulate the temperature of heatspreaders 2216. Thermometers 2220 could, for example, be selected fromthermistors, metallic resistive temperature detectors, thermocouples andthe like.

FIG. 22C shows another example of implementing the co-locatedtemperature control zones and associated heat spreaders that aredescribed in FIG. 22A. In this example, heater elements 2218 may bethermoelectric heat pumps (e.g., Peltier device) that are used tocontrol the flow of heat between adjacent heat spreaders 2216 and one ormore ambient heatsinks 2222, e.g., heatssinks 2222 a and 2222 b. In thisexample, eight heater elements 2218, e.g., heater elements 2218 athrough 2218 h may be used to control the flow of heat between adjacentheat spreaders 2216 and heatsinks 2222. Heater elements 2218 may, forexample, be thin film Peltier devices, such as the Peltier devicescommercially available from Nextreme.

FIG. 23A illustrates a top view of an example of a portion of a dropletactuator 2300 and illustrate a method for manipulating or controlling atemperature gradient along a path of droplet operations electrodes. Inthis example, controlled thermal resistance is provided by the geometryof a copper heat spreading pad (heat spreader) relative to thesurrounding dielectric material (e.g., FR4 with high thermalresistance). The copper heat spreading pad is used to form a temperaturegradient along a path of droplet operations electrodes within atemperature control zone on a droplet actuator. Any suitable heat sourcemay be applied to the heat spreading pad.

Droplet actuator 2300 may include a bottom substrate 2310. Bottomsubstrate 2310 may, for example, be a PCB that includes a dielectriclayer such as FR4. Bottom substrate 2310 may include an arrangement ofdroplet operations electrodes 2312 (e.g., electrowetting electrodes).Droplet operations are conducted atop droplet operations electrodes 2312on a droplet operations surface. Bottom substrate 2310 may also includea heat spreader 2314 for controlling the flow of heat within a certaintemperature control region (not shown).

In one example, heat spreader 2314 is a copper heat spreading pad.Further, heat spreader 2314 may be provided on a different PCB layer asdroplet operations electrodes 2312 (e.g., backside layer or layeradjacent to electrode layer). In another example, heat spreader 2314 maybe provided on the same PCB layer as droplet operations electrodes 2312.Heat spreader 2314 may be formed in a V-shape such that a temperaturegradient is formed along a path of droplet operations electrodes 2312.Heat spreader 2314 may, for example, be heated using a single heatingelement (not shown). In some embodiments, the heat spreading pad or padshave a shape and/or arrangement selected to produce a substantiallylinear gradient along a path of droplet operations electrodes. In someembodiments, heat spreaders are shaped in the form of a “U” and arrangedsuch that a temperature gradient is formed along the path of dropletoperations electrodes, wherein one or more heater elements is coupled toeach “U” shaped heat spreader.

In one example, a single heating element 2313 may be positioned at thenarrow end of the V-shaped heat spreader 2314. The temperature of heatspreader 2314 is substantially the same along the V-shaped geometry ofheat spreader 2314. As the distance from droplet operations electrodes2312 to heat spreader 2314 increases, the thermal resistance provided bythe dielectric material (e.g., FR4) on bottom substrate 2310 increasesand a predictable and linear temperature gradient may be formed. In oneexample, the temperature gradient along droplet operations 2312 maychange in 10-degree increments at each droplet operations electrode2312. For example, the temperature gradient may change from about 100 DCat the narrow end of the V-shaped heat spreader 2314 to about 60° C. atthe wide end of the V-shaped heat spreader 2314.

FIG. 23B illustrates a top view of an example of a portion of a dropletactuator 2350 that includes an arrangement of multiple heat spreaders2314 that are described in FIG. 23A. In this example, an arrangement ofone or more heat spreaders 2314 and corresponding droplet operationselectrodes 2312 are aligned in tandem on droplet actuator 2350.

FIG. 24 illustrates a top view of an example of a portion of a dropletactuator 2400 and illustrates another method for forming a temperaturegradient along a path of droplet operations electrodes. In this example,the dimensions of a copper heat spreading pad (heat spreader) may beused to control the thermal resistance along a path of dropletoperations electrodes and establish a temperature gradient. Bycontrolling the width of the copper trace, e.g., from about 1 mm toabout 0.5 mm wide, the amount of heat loss may be controlled along thepath of droplet operations electrodes.

Droplet actuator 2400 may include a bottom substrate 2410. Bottomsubstrate 2410 may, for example, be a PCB. Bottom substrate 2410 mayinclude an arrangement of droplet operations electrodes 2412 (e.g.,electrowetting electrodes). Droplet operations are conducted atopdroplet operations electrodes 2412 on a droplet operations surface. Aheat spreader 2414 may be provided on bottom substrate 2410 forcontrolling the flow of heat within a certain temperature control region(not shown). In one example, heat spreader 2414 is a copper heatspreading pad. Heat spreader 2414 may be a V-shaped copper trace formedof segments 2416, 2418, and 2420. In one example, segment 2420 of theV-shaped heat spreader 2414 may, for example, be from about 1 mm toabout 0.5 mm wide. Heat spreader 2414 may, for example, be heated usinga single heating element 2422 positioned in proximity to segment 2418 ofthe V-shaped heat spreader 2414.

The arrangement of heat spreader 2414 is such that a temperaturegradient is formed along a path of droplet operations electrodes 2412.In one example, heating element 2422 may be used to heat segment 2418 toa temperature of about 100° C. As segment 2418 is heated, heat isconducted along segment 2420 to segment 2416 and a temperature gradientis formed between segment 2418 and 2416. The temperature gradient may,for example, change from about 100° C. at segment 2418 to about 50° C.at segment 2416 of heat spreader 2414.

Heat from segment 2418 may also be conducted by droplet operationselectrodes 2412. Thermal resistance in this heat conducting pathway maybe dominated by the gaps between each droplet operations electrode 2412,where heat must flow through the dielectric material, e.g., FR4, withhigh thermal resistance. In one example, the gaps between each dropletoperations electrode 2412 may be about 0.127 mm.

In another embodiment, one or more heat sinks (not shown) along thearrangement of droplet operations electrodes 2412 may be used to controlthe flow of heat on droplet actuator 2400.

7.8 Heat Transfer

The invention provides devices and methods for generating heatoff-actuator and transferring the heat to designated temperature controlzones on a droplet actuator. In one embodiment, the invention providesdevices and methods for generating resistive heat off-actuator andtransferring the heat to certain temperature control zones on a dropletactuator. In another embodiment, the invention provides devices andmethods for transferring radiative heat to certain temperature controlzones on a droplet actuator. Alternatively, heat may be generated at asurface of the droplet operations substrate using surface mountedresistors which are mounted to the substrate itself.

7.8.1 Resistive Heat Transfer

In one example, a resistive heater mounted to a spring-loaded bulkmetallic conductor (e.g., aluminum cylinder) may be used to generate andtransfer heat to a designated temperature control zone on a dropletactuator. FIG. 25 illustrates a perspective view of a resistive heatingdevice 2500 that includes resistive heaters mounted to spring-loadedmetallic conductors. Heating device 2500 may include a mechanicalsupport or body 2510 that includes one or more openings 2512 ofsufficient size and shape (e.g. cylindrical shape) to accommodate one ormore heater assemblies 2514, respectively. Mechanical support or body2510 may, for example, be formed of a plastic material. In oneembodiment, three openings 2512 are provided in mechanical support orbody 2510 to accommodate three heater assemblies 2514 a, 2514 b, and2514 c. Each heater assembly 2514 may include a resistive heater 2516that is attached to a bulk metallic conductor 2518, Metallic conductor2518 may, for example, be an aluminum cylinder. Metallic conductor 2518with resistive heater 2516 attached thereto may be mounted on a spring2520 positioned in opening 2512. In operation, spring 2520 is used tohold heater assembly 2514 by spring force against the outside surface ofthe bottom substrate of a droplet actuator (not shown). Heat fromresistive heater 2516 is transferred through metallic conductor 2518 toa temperature control zone on a droplet actuator (not shown).

In another example, a heater device that includes a flex heater with acopper heat spreader may be used to generate and control heat transferto a designated temperature control zone on a droplet actuator. Examplesof flexible heater circuits include polyimide heaters, such as KAPTON®polyimide heaters; silicone rubber heaters (foil); silicone rubberheaters (wire-wound); thermal-clear transparent heaters; mica heaters;all-polyimide heaters; and PTFE (TEFLON™) heaters; all available fromMinco, Inc., Minneapolis, Minn.

In this example, an elastomeric pad (e.g., a neoprene pad or a rubberpad) coupled with a rigid support (e.g., delrin, aluminum) may be usedto position and contact the flex heater circuit to the bottom substrate(e.g. the PCB) of a droplet actuator.

FIG. 26 illustrate a perspective view of another example of a heatingdevice 2600. In this example, heating device 2600 includes one or moreflex heater assemblies. Heater device 2600 may include a rigid supportor body 2610 that has one or more openings or clearance regions foraccepting one or more flex heater assemblies 2612 that are mounted onrespective elastomeric pads 2618 The elastomeric pads 2618 are fittedinto the respective openings or clearance regions of rigid support orbody 2610. Rigid support or body 2610 may, for example, be formed of arigid material, such as delrin, aluminum, and plastic. Elastomeric pads2618 may, for example, be formed of neoprene or rubber.

In one embodiment, three openings or clearance regions are provided inrigid support or body 2610 to accept three flex heater assemblies 2612a, 2612 b, and 2612 c and their respective elastomeric pads 2618 a, 2618b, and 2618 c. Each flex heater assembly 2612 may include a flexiblelead 2614 for making an electrical connection to a heater circuit 2616.In one example, each heater circuit 2616 may be a flex heater circuitwith an integrated copper heat spreader. Because flex heater circuitsmay be custom made, the polyimide dielectric layer may be patterned withother highly resistive metallic materials such as constantan, stainlesssteel, or inconel. By using highly resistive materials, a large amountof heat may be generated in a small area of the droplet actuator. Theelastomeric pads 2618 are used to support the heater circuit 2616-end offlex heater assemblies 2612.

The positions of flex heater assemblies 2612 in rigid support or body2610 correspond to the positions of heating zones of a droplet actuator(not shown) for which heating device 2600 is designed. In operation, theheater circuits 2616 of flex heater assemblies 2612 of heating device2600 are pressed against, for example, the bottom substrate of thedroplet actuator. In this way, heat from each heater circuit 2616 istransferred directly to a corresponding temperature control zone of thedroplet actuator. Portions of rigid support body may also be used tosupport other bodies used for integrated functions, such as manipulationof magnetic beads in the droplet operations gap.

In yet another example, resistive heat transfer may be accomplishedthrough spring pins connecting an electrowetting effector board anddroplet actuator. The electrowetting effector board includes an array ofsmall spring pins that make electrical contact with the microfluidicchip. The electrowetting effector board communicates the signals thatcontrol droplet movement from the instrument to the droplet actuator. Anexample of an electrowetting effector board is described below in FIGS.27A and 27B.

FIGS. 27A and 27B illustrate side views of an example of a portion of anelectrowetting effector board 2700 configured for generation ofresistive heat and illustrate the alignment of the effector board with adroplet actuator for resistive heat transfer. As shown in FIG. 27 A,electrowetting effector board 2710 may, for example, be a PCB thatincludes a copper trace 2712 and a spring pin 2714. A heating element2716 may be electrically coupled to copper trace 2712. Heating element2716 may, for example, be a Kapton flex heater or a typical foil or thinfilm resistor.

Referring to FIG. 27B, electrowetting effector board 2700 may be alignedwith a droplet actuator 2718. Droplet actuator 2718 may, for example,include a PCB that includes a copper trace 2720. Copper trace 2720 may,for example, be positioned with a certain temperature control zone ofdroplet actuator 2718. The alignment of electrowetting effector board2700 and droplet actuator 2718 is such that spring pin 2714 contactscopper trace 2720. As spring pin 2714 makes contact with copper trace2720, heat generated from heating element 2716 is transferred to coppertrace 2720 of droplet actuator 2718.

In another example, a different set of spring pins may be used forresistive heat transfer. In this example, effector board 2700 may be aseparate heater board.

7.8.2 Radiative Heat Transfer

The invention provides devices and methods for transferring radiativeheat to certain temperature control zones on a droplet actuator. Becauseradiative heat is used, contact between a heat source and the dropletactuator is not required.

FIG. 28 illustrates a side view of an example of a portion of a dropletactuator 2800 that is configured for radiative heat transfer to atemperature control zone on a droplet actuator. Droplet actuator 2800may include a bottom substrate 2810. Bottom substrate 2810 may, forexample, be a PCB that includes a dielectric layer 2812 (e.g., FR4). Atleast one droplet operations electrode 2814 (e.g., electrowettingelectrode) may be patterned atop dielectric layer 2812. A heat conductor2816 may be patterned on the backside of dielectric layer 2812 andopposite from droplet operations electrode 2814. Heat conductor 2816may, for example, be a copper heat conductor. Droplet operationselectrode 2814 and heat conductor 2816 are thermally connected by a via2818, which may be a copper via. Attached (bonded) to heat conductor2816 is a blackbody 2820. Blackbody 2820 may, for example, be aninfrared (IR) absorbing blackbody. An infrared heat source 2822 may bepositioned in proximity (e.g., about 2 mm from) blackbody 2820. Heatsource 2822 may, for example, be a laser diode or an IR LED.

In operation, infrared radiation from heat source 2822 is absorbed byblackbody 2820 and transferred as heat through heat conductor 2816 andvia 2818 to droplet operations electrode 2814. As with all otherembodiments of the invention, thermometer (not shown) may be attached(e.g., taped using tape) to conductor 2816 and used to monitortemperature.

7.9 Temperature Control by Droplet Positioning

The invention provides method for controlling the temperature of adroplet by transporting the droplet from one temperature region toanother temperature control region (position dithering) on a dropletactuator. By repeatedly transporting a droplet between temperatureregions (e.g., two temperature regions), a droplet temperature may beachieved that is between the temperatures of the two temperatureregions.

FIG. 29A illustrates an example of a portion of a droplet actuator 2900for controlling the temperature of a droplet by position dithering.Droplet actuator 2900 may include a bottom substrate 2910. Bottomsubstrate 2910 may, for example, be a PCB. Bottom substrate 2910 mayinclude an arrangement of droplet operations electrodes 2912 (e.g.,electrowetting electrodes). Droplet operations are conducted atopdroplet operations electrodes 2912 on a droplet operations surface.Droplet actuator 2900 may include one or more temperature regions 2914,e.g., two temperature regions 2914 a and 2914 b. Temperature regions2914 a and 2914 b may be separated spatially to achieve a thermalgradient between the two zones. The temperature of a droplet may becontrolled and maintained by positioning the droplet at a certainlocation along the thermal gradient between the two temperature regions2914 a and 2914 b. Bottom substrate 2910 may include one or more heatspreaders (copper heat spreading pads) 2916, e.g., heat spreaders 2916 aand 2916 b, for controlling the flow of heat within associatedtemperature regions 2914 a and 2914 b.

In one example, temperature region 2914 a may be heated to a temperatureof about 100° C. Temperature region 2914 b may be heated to atemperature of about 60° C. Because of the thermal gradient betweentemperature regions 2914 a and 2914 b, a certain droplet operationselectrode 2912 located therebetween and along the thermal gradient maybe at an intermediate temperature relative to temperature regions 2914 aand 2914 b. FIGS. 29B and 29C below are examples of schematic diagramsrelated to the thermal control of droplet actuator 2900.

FIG. 29B illustrates a schematic diagram of an example of a thermalcircuit 2950 for droplet actuator 2900 of FIG. 29A that is configuredfor position dithering. Thermal circuit 2950 is an example of a circuitrepresenting the thermal gradient between, for example, the twotemperature regions 2914 a and 2914 b. For example, T_(HOT) may be 100°C., which is the temperature at temperature region 2914 a, and T_(COLD)may be 60° C., which is the temperature at temperature region 2914 b.

FIG. 29C illustrates a schematic view of an example of an electricalequivalent circuit 2970 for position dithering used for droplettemperature control on droplet actuator 2900 of FIG. 29 A. Electricalequivalent circuit 2970 represents position dithering as a means ofdroplet temperature control. In one example, C_(COPPER)=0.15 C_(DROPLET)to 0.5 C_(DROPLET), where the larger number may account for other copperconnected to the droplet operations electrode through, for example, avia. The following observations may be made: A sizable voltage can bedeveloped at V₁ R_(AMBIENT) is relatively high or if a large current(heat flux) is pushed. R_(AMBIENT) is the overall resistance toelectrical ground. R_(POLYIMIDE) will typically keep V₁ from everreaching V_(COLD) (or V_(HOT) when switched to that path). There will besome loss across the dielectric layer. The C_(COPPER) capacitorstypically charge about 2 times to about 6.5 times faster than theCDROPLET capacitor. In order to prevent V₁ from experiencing temperatureexcursions near V_(HOT) and V_(COLD) (which may be important for PCR andother thermal control applications), the switching speed of the dropletbetween two positions may need to be significantly faster then theC_(DROPLET) time constant. Otherwise, the temperature excursions need tobe controlled by setting V_(HOT) and V_(COLD).

7.10 Systems

Referring to FIGS. 1 through 30, it will be appreciated that variousaspects of the invention may be embodied as a method, system, orcomputer program product. Aspects of the invention may take the form ofhardware embodiments, software embodiments (including firmware, residentsoftware, micro-code, etc.), or embodiments combining software andhardware aspects that may all generally be referred to herein as a“circuit,” “module” or “system.” Furthermore, the methods of theinvention may take the form of a computer program product on acomputer-usable storage medium having computer-usable program codeembodied in the medium.

Any suitable computer useable medium may be utilized for softwareaspects of the invention. The computer-usable or computer-readablemedium may be, for example but not limited to, an electronic, magnetic,optical, electromagnetic, infrared, or semiconductor system, apparatus,device, or propagation medium. More specific examples (a non-exhaustivelist) of the computer-readable medium would include some or all of thefollowing: an electrical connection having one or more wires, a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), an optical fiber, a portable compact disc read-onlymemory (CD-ROM), an optical storage device, a transmission medium suchas those supporting the Internet or an intranet, or a magnetic storagedevice. Note that the computer-usable or computer-readable medium couldeven be paper or another suitable medium upon which the program isprinted, as the program can be electronically captured, via, forinstance, optical scanning of the paper or other medium, then compiled,interpreted, or otherwise processed in a suitable manner, if necessary,and then stored in a computer memory. In the context of this document, acomputer-usable or computer-readable medium may be any medium that cancontain, store, communicate, propagate, or transport the program for useby or in connection with the instruction execution system, apparatus, ordevice.

Computer program code for carrying out operations of the invention maybe written in an object oriented programming language such as Java,Smalltalk, C++ or the like. However, the computer program code forcarrying out operations of the invention may also be written inconventional procedural programming languages, such as the “C”programming language or similar programming languages. The program codemay execute entirely on the user's computer, partly on the user'scomputer, as a stand-alone software package, partly on the user'scomputer and partly on a remote computer or entirely on the remotecomputer or server. In the latter scenario, the remote computer may beconnected to the user's computer through a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Certain aspects of invention are described with reference to variousmethods and method steps. It will be understood that each method stepcan be implemented by computer program instructions. These computerprogram instructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the methods.

The computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instruction meanswhich implement various aspects of the method steps.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing various functions/actsspecified in the methods of the invention.

8 CONCLUDING REMARKS

The foregoing detailed description of embodiments refers to theaccompanying drawings, which illustrate specific embodiments of theinvention. Other embodiments having different structures and operationsdo not depart from the scope of the invention. The term “the invention”or the like is used with reference to certain specific examples of themany alternative aspects or embodiments of the applicants' invention setforth in this specification, and neither its use nor its absence isintended to limit the scope of the applicants' invention or the scope ofthe claims. This specification is divided into sections for theconvenience of the reader only. Headings should not be construed aslimiting of the scope of the invention. The definitions are intended asa part of the description of the invention. It will be understood thatvarious details of the invention may be changed without departing fromthe scope of the invention. Furthermore, the foregoing description isfor the purpose of illustration only, and not for the purpose oflimitation.

I claim:
 1. A droplet actuator device comprising: a. a bottom substrateand a top substrate separated from each other to form a gaptherebetween; b. an arrangement of droplet operations electrodes on oneof or both of the bottom and/or top substrates configured for conductingdroplet operations thereon; and c. one or more heat-spreader-expandedtemperature control zones in the gap, wherein each of the one or moreheat-expanded temperature zones is established by at least: (i) one ormore heater elements in proximity to and aligned with one or more of thedroplet operations electrodes in the arrangement of droplet operationselectrodes in a manner which permits establishment of temperaturecontrol in the gap in the vicinity of the one or more droplet operationselectrodes; and (ii) a heat spreader comprising a metal layer structureincluded with one of or both of the bottom and/or top substrates anddistinct from the droplet operations electrodes, wherein the heatspreader is arranged to spread heat generated from the one or moreheater elements along a droplet operations electrode path comprising theone or more droplet operations electrodes, and wherein the heat spreaderis distinct from the one or more heater elements and is configured tospread heat and maintain a more uniform temperature gradient within theone or more heat-spreader-expanded temperature control zones relative toa corresponding droplet actuator device lacking the heat spreader. 2.The droplet actuator device of claim 1, wherein the bottom substratecomprises a PCB.
 3. The droplet actuator device of claim 2, wherein thePCB comprises a dielectric layer.
 4. The droplet actuator device ofclaim 1, wherein the arrangement of droplet operations electrodescomprise electrowetting electrodes.
 5. The droplet actuator device ofclaim 2, wherein the arrangement of droplet operations electrodes arearranged on the PCB, and the heat spreader and the arrangement ofdroplet operations electrodes are provided on a same layer on the PCB.6. The droplet actuator device of claim 1, wherein the heat spreader iscopper.
 7. The droplet actuator device of claim 5, wherein the heatspreader is positioned adjacent to the one or more droplet operationselectrodes.
 8. The droplet actuator device of claim 2, wherein thearrangement of droplet operations electrodes are arranged in a layer onthe PCB, and the heat spreader is provided on a different layer on thePCB than the arrangement of droplet operations electrodes.
 9. Thedroplet actuator device of claim 8, wherein the heat spreader isprovided on a layer on a backside of the PCB that is opposite to thelayer of the arrangement of droplet operations electrodes.
 10. Thedroplet actuator device of claim 8, wherein the heat spreader isprovided on a layer on the PCB adjacent to the arrangement of dropletoperations electrodes arranged on the PCB.
 11. The droplet actuatordevice of claim 1, comprising at least two heat-spreader-expandedtemperature control zones, wherein the heat spreaders are configured toheat the at least two heat-spreader-expanded temperature control zonesto a same or different temperatures.
 12. The droplet actuator device ofclaim 11, wherein the at least two heat-spreader-expanded temperaturecontrol zones heated to the same temperature are thermally coupled. 13.The droplet actuator device of claim 1, wherein the one or more heaterelements provide heat to the heat spreader.
 14. The droplet actuatordevice of claim 8, wherein the one or more heater elements arepositioned directly underneath the heat spreader.
 15. The dropletactuator device of claim 1, wherein one or more of the one or moreheater elements comprises a resistive heater.
 16. The droplet actuatordevice of claim 1, wherein the one or more heater elements comprisethermoelectric heat pumps.
 17. The droplet actuator device of claim 1,further comprising thermistors to monitor and regulate the temperatureof the heat spreader.
 18. The droplet actuator device of claim 1,wherein the heat spreader is shaped to form a temperature gradient alonga path of the one or more droplet operations electrodes.
 19. The dropletactuator device of claim 18, wherein the heat spreader is shaped in theform of a “V” such that a substantially linear temperature gradient isformed along the path of the one or more droplet operations electrodes,wherein one of the one or more heater elements is positioned at thenarrow end of the “V” shaped heat spreader.
 20. The droplet actuatordevice of claim 18, wherein the heat spreader is shaped in the form of a“U” and arranged such that a temperature gradient is formed along thepath of the one or more droplet operations electrodes, wherein one ofthe one or more heater elements is coupled to the “U” shaped heatspreader.
 21. The droplet actuator device of claim 1, wherein the gapcomprises oil.
 22. The droplet actuator device of claim 1, wherein thegap comprises silicone oil.